--- a/devtools/client/themes/webconsole.css
+++ b/devtools/client/themes/webconsole.css
@@ -989,16 +989,21 @@ a.learn-more-link.webconsole-learn-more-
 
 /* The bubble that shows the number of times a message is repeated */
 .webconsole-output-wrapper .message-repeats {
   background-color: var(--repeat-bubble-background-color);
   font-weight: normal;
   font-size: 0.8em;
 }
 
+/* Prefix text that can be set by ConsoleAPI option */
+.webconsole-output-wrapper .console-message-prefix {
+  color: var(--theme-comment);
+}
+
 /* Network Messages */
 
 .webconsole-output-wrapper .message.network .method {
   margin-inline-end: 5px;
 }
 
 .webconsole-output-wrapper .message.network .xhr {
   background-color: var(--theme-comment);

--- a/devtools/client/webconsole/new-console-output/components/message-types/ConsoleApiCall.js
+++ b/devtools/client/webconsole/new-console-output/components/message-types/ConsoleApiCall.js
@@ -46,16 +46,17 @@ function ConsoleApiCall(props) {
     source,
     type,
     level,
     stacktrace,
     frame,
     timeStamp,
     parameters,
     messageText,
+    prefix,
     userProvidedStyles,
   } = message;
 
   let messageBody;
   const messageBodyConfig = {
     dispatch,
     messageId,
     parameters,
@@ -69,16 +70,21 @@ function ConsoleApiCall(props) {
   } else if (type === "assert") {
     let reps = formatReps(messageBodyConfig);
     messageBody = dom.span({ className: "cm-variable" }, "Assertion failed: ", reps);
   } else if (type === "table") {
     // TODO: Chrome does not output anything, see if we want to keep this
     messageBody = dom.span({className: "cm-variable"}, "console.table()");
   } else if (parameters) {
     messageBody = formatReps(messageBodyConfig);
+    if (prefix) {
+      messageBody.unshift(dom.span({
+        className: "console-message-prefix"
+      }, `${prefix}: `));
+    }
   } else {
     messageBody = messageText;
   }
 
   let attachment = null;
   if (type === "table") {
     attachment = ConsoleTable({
       dispatch,

--- a/devtools/client/webconsole/new-console-output/reducers/messages.js
+++ b/devtools/client/webconsole/new-console-output/reducers/messages.js
@@ -698,16 +698,18 @@ function passSearchFilters(message, filt
     // Look for a match in net events.
     || isTextInNetEvent(text, message.request)
     // Look for a match in stack-trace.
     || isTextInStackTrace(text, message.stacktrace)
     // Look for a match in messageText.
     || isTextInMessageText(text, message.messageText)
     // Look for a match in notes.
     || isTextInNotes(text, message.notes)
+    // Look for a match in prefix.
+    || isTextInPrefix(text, message.prefix)
   );
 }
 
 /**
 * Returns true if given text is included in provided stack frame.
 */
 function isTextInFrame(text, frame) {
   if (!frame) {
@@ -800,16 +802,27 @@ function isTextInNotes(text, notes) {
     (
       note.messageBody &&
       note.messageBody.toLocaleLowerCase().includes(text.toLocaleLowerCase())
     )
   );
 }
 
 /**
+* Returns true if given text is included in prefix.
+*/
+function isTextInPrefix(text, prefix) {
+  if (!prefix) {
+    return false;
+  }
+
+  return `${prefix}: `.toLocaleLowerCase().includes(text.toLocaleLowerCase());
+}
+
+/**
  * Get a flat array of all the grips and their properties.
  *
  * @param {Array} Grips
  * @return {Array} Flat array of the grips and their properties.
  */
 function getAllProps(grips) {
   let result = grips.reduce((res, grip) => {
     let previewItems = getGripPreviewItems(grip);

--- a/devtools/client/webconsole/new-console-output/test/components/console-api-call.test.js
+++ b/devtools/client/webconsole/new-console-output/test/components/console-api-call.test.js
@@ -14,16 +14,17 @@ const { setupStore } = require("devtools
 
 // Components under test.
 const ConsoleApiCall = createFactory(require("devtools/client/webconsole/new-console-output/components/message-types/ConsoleApiCall"));
 const {
   MESSAGE_OPEN,
   MESSAGE_CLOSE,
 } = require("devtools/client/webconsole/new-console-output/constants");
 const { INDENT_WIDTH } = require("devtools/client/webconsole/new-console-output/components/MessageIndent");
+const {prepareMessage} = require("devtools/client/webconsole/new-console-output/utils/messages");
 
 // Test fakes.
 const { stubPreparedMessages } = require("devtools/client/webconsole/new-console-output/test/fixtures/stubs/index");
 const serviceContainer = require("devtools/client/webconsole/new-console-output/test/fixtures/serviceContainer");
 
 describe("ConsoleAPICall component:", () => {
   describe("console.log", () => {
     it("renders string grips", () => {
@@ -82,16 +83,47 @@ describe("ConsoleAPICall component:", ()
       const secondElementStyle = elements.eq(1).prop("style");
       expect(secondElementStyle.color).toBe(undefined);
 
       const thirdElementStyle = elements.eq(2).prop("style");
       // Allowed styles are applied accordingly on the third element.
       expect(thirdElementStyle.color).toBe("blue");
     });
 
+    it("renders prefixed messages", () => {
+      const stub = {
+        "level": "debug",
+        "filename": "resource:///modules/CustomizableUI.jsm",
+        "lineNumber": 181,
+        "functionName": "initialize",
+        "timeStamp": 1519311532912,
+        "arguments": [
+          "Initializing"
+        ],
+        "prefix": "MyNicePrefix",
+        "workerType": "none",
+        "styles": [],
+        "category": "webdev",
+        "_type": "ConsoleAPI"
+      };
+      const wrapper = render(ConsoleApiCall({
+        message: prepareMessage(stub, {getNextId: () => "p"}),
+        serviceContainer
+      }));
+      const prefix = wrapper.find(".console-message-prefix");
+      expect(prefix.text()).toBe("MyNicePrefix: ");
+
+      expect(wrapper.find(".message-body").text()).toBe("MyNicePrefix: Initializing");
+
+      // There should be the location
+      const locationLink = wrapper.find(`.message-location`);
+      expect(locationLink.length).toBe(1);
+      expect(locationLink.text()).toBe("CustomizableUI.jsm:181");
+    });
+
     it("renders repeat node", () => {
       const message = stubPreparedMessages.get("console.log('foobar', 'test')");
       const wrapper = render(ConsoleApiCall({
         message,
         serviceContainer,
         repeat: 107
       }));
 

--- a/devtools/client/webconsole/new-console-output/test/components/message-location.test.js
+++ b/devtools/client/webconsole/new-console-output/test/components/message-location.test.js
@@ -35,17 +35,17 @@ describe("Message - location element", (
     expect(locationLink.text()).toBe("test-console-api.html:1:27");
 
     locationLink.simulate("click");
 
     expect(onViewSourceInDebugger.calledOnce).toBe(true);
     expect(onViewSource.notCalled).toBe(true);
   });
 
-  it.only("Calls onViewSource when clicked and onViewSourceInDebugger undefined", () => {
+  it("Calls onViewSource when clicked and onViewSourceInDebugger undefined", () => {
     const onViewSource = sinon.spy();
 
     const message = stubPreparedMessages.get("console.log('foobar', 'test')");
 
     const wrapper = mount(MessageContainer({
       getMessage: () => message,
       serviceContainer: Object.assign({}, serviceContainer, {
         onViewSource,

--- a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js
+++ b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/consoleApi.js
@@ -32,17 +32,18 @@ stubPreparedMessages.set(`console.log('f
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log(undefined)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924479,
   "type": "log",
@@ -60,17 +61,18 @@ stubPreparedMessages.set(`console.log(un
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.warn('danger, will robinson!')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924487,
   "type": "warn",
@@ -86,17 +88,18 @@ stubPreparedMessages.set(`console.warn('
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log(NaN)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924495,
   "type": "log",
@@ -114,17 +117,18 @@ stubPreparedMessages.set(`console.log(Na
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log(null)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924501,
   "type": "log",
@@ -142,17 +146,18 @@ stubPreparedMessages.set(`console.log(nu
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('鼬')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924506,
   "type": "log",
@@ -168,17 +173,18 @@ stubPreparedMessages.set(`console.log('鼬')`, new ConsoleMessage({
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.clear()`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924512,
   "type": "clear",
@@ -194,17 +200,18 @@ stubPreparedMessages.set(`console.clear(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924515,
   "type": "log",
@@ -218,17 +225,18 @@ stubPreparedMessages.set(`console.count(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.assert(false, {message: 'foobar'})`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924521,
   "type": "assert",
@@ -274,17 +282,18 @@ stubPreparedMessages.set(`console.assert
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('hello \nfrom \rthe \"string world!')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924528,
   "type": "log",
@@ -300,17 +309,18 @@ stubPreparedMessages.set(`console.log('h
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('úṇĩçödê țĕșť')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924586,
   "type": "log",
@@ -326,17 +336,18 @@ stubPreparedMessages.set(`console.log('úṇĩçödê țĕșť')`, new ConsoleMessage({
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.dirxml(window)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924596,
   "type": "log",
@@ -364,17 +375,18 @@ stubPreparedMessages.set(`console.dirxml
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('myarray', ['red', 'green', 'blue'])`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924604,
   "type": "log",
@@ -408,17 +420,18 @@ stubPreparedMessages.set(`console.log('m
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('myregex', /a.b.c/)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924610,
   "type": "log",
@@ -444,17 +457,18 @@ stubPreparedMessages.set(`console.log('m
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.table(['red', 'green', 'blue']);`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924612,
   "type": "table",
@@ -487,17 +501,18 @@ stubPreparedMessages.set(`console.table(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('myobject', {red: 'redValue', green: 'greenValue', blue: 'blueValue'});`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924614,
   "type": "log",
@@ -549,17 +564,18 @@ stubPreparedMessages.set(`console.log('m
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.debug('debug message');`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924621,
   "type": "debug",
@@ -575,17 +591,18 @@ stubPreparedMessages.set(`console.debug(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.info('info message');`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924625,
   "type": "info",
@@ -601,17 +618,18 @@ stubPreparedMessages.set(`console.info('
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.error('error message');`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924628,
   "type": "error",
@@ -634,17 +652,18 @@ stubPreparedMessages.set(`console.error(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('mymap')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924631,
   "type": "log",
@@ -683,17 +702,18 @@ stubPreparedMessages.set(`console.log('m
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 5,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log('myset')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924746,
   "type": "log",
@@ -726,17 +746,18 @@ stubPreparedMessages.set(`console.log('m
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.trace()`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924752,
   "type": "trace",
@@ -769,17 +790,18 @@ stubPreparedMessages.set(`console.trace(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 3
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.time('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924757,
   "type": "nullMessage",
@@ -793,17 +815,18 @@ stubPreparedMessages.set(`console.time('
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`timerAlreadyExists`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924758,
   "type": "time",
@@ -817,17 +840,18 @@ stubPreparedMessages.set(`timerAlreadyEx
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.timeEnd('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924759,
   "type": "timeEnd",
@@ -841,17 +865,18 @@ stubPreparedMessages.set(`console.timeEn
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 4,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`timerDoesntExist`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924759,
   "type": "timeEnd",
@@ -865,17 +890,18 @@ stubPreparedMessages.set(`timerDoesntExi
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 5,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.table('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924801,
   "type": "log",
@@ -891,17 +917,18 @@ stubPreparedMessages.set(`console.table(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.table(['a', 'b', 'c'])`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924859,
   "type": "table",
@@ -934,17 +961,18 @@ stubPreparedMessages.set(`console.table(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.group('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924863,
   "type": "startGroup",
@@ -960,17 +988,18 @@ stubPreparedMessages.set(`console.group(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupEnd('bar')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924864,
   "type": "endGroup",
@@ -984,17 +1013,18 @@ stubPreparedMessages.set(`console.groupE
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupCollapsed('foo')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924870,
   "type": "startGroupCollapsed",
@@ -1010,17 +1040,18 @@ stubPreparedMessages.set(`console.groupC
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupEnd('foo')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924871,
   "type": "endGroup",
@@ -1034,17 +1065,18 @@ stubPreparedMessages.set(`console.groupE
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.group()`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924878,
   "type": "startGroup",
@@ -1060,17 +1092,18 @@ stubPreparedMessages.set(`console.group(
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupEnd()`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924879,
   "type": "endGroup",
@@ -1084,17 +1117,18 @@ stubPreparedMessages.set(`console.groupE
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log(%cfoobar)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924883,
   "type": "log",
@@ -1114,17 +1148,18 @@ stubPreparedMessages.set(`console.log(%c
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [
     "color:blue; font-size:1.3em; background:url('http://example.com/test'); position:absolute; top:10px; ",
     "color:red; line-height: 1.5; background:url('http://example.com/test')"
   ],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.log("%cHello%c|%cWorld")`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1518681614352,
   "type": "log",
@@ -1146,17 +1181,18 @@ stubPreparedMessages.set(`console.log("%
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [
     "color:red",
     "",
     "color: blue"
   ],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.group(%cfoo%cbar)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924887,
   "type": "startGroup",
@@ -1176,17 +1212,18 @@ stubPreparedMessages.set(`console.group(
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [
     "color:blue;font-size:1.3em;background:url('http://example.com/test');position:absolute;top:10px",
     "color:red;background:url('http://example.com/test')"
   ],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupEnd(%cfoo%cbar)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924887,
   "type": "endGroup",
@@ -1200,17 +1237,18 @@ stubPreparedMessages.set(`console.groupE
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 6,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupCollapsed(%cfoo%cbaz)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924892,
   "type": "startGroupCollapsed",
@@ -1230,17 +1268,18 @@ stubPreparedMessages.set(`console.groupC
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [
     "color:blue;font-size:1.3em;background:url('http://example.com/test');position:absolute;top:10px",
     "color:red;background:url('http://example.com/test')"
   ],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.groupEnd(%cfoo%cbaz)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924893,
   "type": "endGroup",
@@ -1254,17 +1293,18 @@ stubPreparedMessages.set(`console.groupE
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 6,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.dir({C, M, Y, K})`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924899,
   "type": "dir",
@@ -1321,17 +1361,18 @@ stubPreparedMessages.set(`console.dir({C
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 27
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | default: 1`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913333,
   "type": "log",
@@ -1345,17 +1386,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 2,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | default: 2`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913334,
   "type": "log",
@@ -1369,17 +1411,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | test counter: 1`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913334,
   "type": "log",
@@ -1393,17 +1436,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 4,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | test counter: 2`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913334,
   "type": "log",
@@ -1417,17 +1461,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 5,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | default: 3`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913334,
   "type": "log",
@@ -1441,17 +1486,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 6,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | clear`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913334,
   "type": "clear",
@@ -1467,17 +1513,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 7,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | default: 4`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913335,
   "type": "log",
@@ -1491,17 +1538,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 8,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`console.count | test counter: 3`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1511365913335,
   "type": "log",
@@ -1515,17 +1563,18 @@ stubPreparedMessages.set(`console.count 
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 9,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": null,
   "userProvidedStyles": [],
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPackets.set(`console.log('foobar', 'test')`, {
   "from": "server1.conn0.child1/consoleActor2",
   "type": "consoleAPICall",
   "message": {
     "addonId": "",
     "arguments": [

--- a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/cssMessage.js
+++ b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/cssMessage.js
@@ -28,17 +28,18 @@ stubPreparedMessages.set(`Unknown property ‘such-unknown-property’.  Declaration dropped.`, new ConsoleMessage({
   "frame": {
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-css-message.html",
     "line": 3,
     "column": 25
   },
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`Error in parsing value for ‘padding-top’.  Declaration dropped.`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "css",
   "timeStamp": 1479159920465,
   "type": "log",
@@ -51,17 +52,18 @@ stubPreparedMessages.set(`Error in parsing value for ‘padding-top’.  Declaration dropped.`, new ConsoleMessage({
   "frame": {
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-css-message.html",
     "line": 3,
     "column": 16
   },
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPackets.set(`Unknown property ‘such-unknown-property’.  Declaration dropped.`, {
   "from": "server1.conn0.child1/consoleActor2",
   "type": "pageError",
   "pageError": {
     "errorMessage": "Unknown property ‘such-unknown-property’.  Declaration dropped.",
     "errorMessageName": "",

--- a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/evaluationResult.js
+++ b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/evaluationResult.js
@@ -36,17 +36,18 @@ stubPreparedMessages.set(`new Date(0)`, 
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"log\",\"parameters\":[{\"type\":\"object\",\"actor\":\"server1.conn0.child1/obj30\",\"class\":\"Date\",\"extensible\":true,\"frozen\":false,\"sealed\":false,\"ownPropertyLength\":0,\"preview\":{\"timestamp\":0}}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`asdf()`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1479159921377,
   "type": "result",
@@ -64,17 +65,18 @@ stubPreparedMessages.set(`asdf()`, new C
     "source": "debugger eval code",
     "line": 1,
     "column": 1
   },
   "groupId": null,
   "exceptionDocURL": "https://developer.mozilla.org/docs/Web/JavaScript/Reference/Errors/Not_defined?utm_source=mozilla&utm_medium=firefox-console-errors&utm_campaign=default",
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`1 + @`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1479159921399,
   "type": "result",
@@ -92,17 +94,18 @@ stubPreparedMessages.set(`1 + @`, new Co
     "source": "debugger eval code",
     "line": 1,
     "column": 4
   },
   "groupId": null,
   "exceptionDocURL": "https://developer.mozilla.org/docs/Web/JavaScript/Reference/Errors/Illegal_character?utm_source=mozilla&utm_medium=firefox-console-errors&utm_campaign=default",
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`inspect({a: 1})`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1499776070751,
   "type": "result",
@@ -135,17 +138,18 @@ stubPreparedMessages.set(`inspect({a: 1}
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"log\",\"parameters\":[{\"type\":\"object\",\"actor\":\"server1.conn0.child1/obj35\",\"class\":\"Object\",\"extensible\":true,\"frozen\":false,\"sealed\":false,\"ownPropertyLength\":1,\"preview\":{\"kind\":\"Object\",\"ownProperties\":{\"a\":{\"configurable\":true,\"enumerable\":true,\"writable\":true,\"value\":1}},\"ownSymbols\":[],\"ownPropertiesLength\":1,\"ownSymbolsLength\":0,\"safeGetterValues\":{}}}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`cd(document)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1510650094657,
   "type": "result",
@@ -158,17 +162,18 @@ stubPreparedMessages.set(`cd(document)`,
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":\"Cannot cd() to the given window. Invalid argument.\",\"parameters\":[{\"type\":\"undefined\"}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`undefined`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1518606917356,
   "type": "result",
@@ -180,17 +185,18 @@ stubPreparedMessages.set(`undefined`, ne
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"log\",\"parameters\":[{\"type\":\"undefined\"}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`longString message Error`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1493108241073,
   "type": "result",
@@ -208,17 +214,18 @@ stubPreparedMessages.set(`longString mes
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":{\"type\":\"longString\",\"initial\":\"Error: Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Long error Lon\",\"length\":110007,\"actor\":\"server1.conn0.child1/longString37\"},\"parameters\":[{\"type\":\"undefined\"}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`eval throw ""`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1517990289517,
   "type": "result",
@@ -231,17 +238,18 @@ stubPreparedMessages.set(`eval throw ""`
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":\"Error\",\"parameters\":[{\"type\":\"undefined\"}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`eval throw "tomato"`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1517990289520,
   "type": "result",
@@ -254,17 +262,18 @@ stubPreparedMessages.set(`eval throw "to
     }
   ],
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":\"Error: tomato\",\"parameters\":[{\"type\":\"undefined\"}],\"source\":\"javascript\",\"type\":\"result\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPackets.set(`new Date(0)`, {
   "from": "server1.conn0.child1/consoleActor2",
   "input": "new Date(0)",
   "result": {
     "type": "object",
     "actor": "server1.conn0.child1/obj30",

--- a/devtools/client/webconsole/new-console-output/test/fixtures/stubs/pageError.js
+++ b/devtools/client/webconsole/new-console-output/test/fixtures/stubs/pageError.js
@@ -60,17 +60,18 @@ stubPreparedMessages.set(`ReferenceError
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 3,
     "column": 5
   },
   "groupId": null,
   "exceptionDocURL": "https://developer.mozilla.org/docs/Web/JavaScript/Reference/Errors/Not_defined?utm_source=mozilla&utm_medium=firefox-console-errors&utm_campaign=default",
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`SyntaxError: redeclaration of let a`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1487992945524,
   "type": "log",
@@ -105,17 +106,18 @@ stubPreparedMessages.set(`SyntaxError: r
       "messageBody": "Previously declared at line 2, column 6",
       "frame": {
         "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
         "line": 2,
         "column": 6
       }
     }
   ],
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`TypeError longString message`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1493109507061,
   "type": "log",
@@ -152,17 +154,18 @@ stubPreparedMessages.set(`TypeError long
   "frame": {
     "source": "http://example.com/browser/devtools/client/webconsole/new-console-output/test/fixtures/stub-generators/test-console-api.html",
     "line": 1,
     "column": 7
   },
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`throw ""`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1517942398629,
   "type": "log",
@@ -171,17 +174,18 @@ stubPreparedMessages.set(`throw ""`, new
   "messageText": "uncaught exception: ",
   "parameters": null,
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":\"uncaught exception: \",\"parameters\":null,\"source\":\"javascript\",\"type\":\"log\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPreparedMessages.set(`throw "tomato"`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1517942398637,
   "type": "log",
@@ -190,17 +194,18 @@ stubPreparedMessages.set(`throw "tomato"
   "messageText": "uncaught exception: tomato",
   "parameters": null,
   "repeatId": "{\"frame\":null,\"groupId\":null,\"indent\":0,\"level\":\"error\",\"messageText\":\"uncaught exception: tomato\",\"parameters\":null,\"source\":\"javascript\",\"type\":\"log\",\"userProvidedStyles\":null}",
   "stacktrace": null,
   "frame": null,
   "groupId": null,
   "userProvidedStyles": null,
   "notes": null,
-  "indent": 0
+  "indent": 0,
+  "prefix": ""
 }));
 
 stubPackets.set(`ReferenceError: asdf is not defined`, {
   "from": "server1.conn0.child1/consoleActor2",
   "type": "pageError",
   "pageError": {
     "errorMessage": "ReferenceError: asdf is not defined",
     "errorMessageName": "JSMSG_NOT_DEFINED",

--- a/devtools/client/webconsole/new-console-output/test/store/filters.test.js
+++ b/devtools/client/webconsole/new-console-output/test/store/filters.test.js
@@ -181,16 +181,47 @@ describe("Filtering", () => {
       store.dispatch(messagesAdd([traceMessage]));
 
       store.dispatch(actions.filterTextSet("search-location-test.js:85:13"));
 
       let messages = getVisibleMessages(store.getState());
       expect(messages.length - numUnfilterableMessages).toEqual(1);
     });
 
+    it("matches prefixed log message", () => {
+      const stub = {
+        "level": "debug",
+        "filename": "resource:///modules/CustomizableUI.jsm",
+        "lineNumber": 181,
+        "functionName": "initialize",
+        "timeStamp": 1519311532912,
+        "arguments": [
+          "Initializing"
+        ],
+        "prefix": "MyNicePrefix",
+        "workerType": "none",
+        "styles": [],
+        "category": "webdev",
+        "_type": "ConsoleAPI"
+      };
+      store.dispatch(messagesAdd([stub]));
+
+      store.dispatch(actions.filterTextSet("MyNice"));
+      let messages = getVisibleMessages(store.getState());
+      expect(messages.length - numUnfilterableMessages).toEqual(1);
+
+      store.dispatch(actions.filterTextSet("MyNicePrefix"));
+      messages = getVisibleMessages(store.getState());
+      expect(messages.length - numUnfilterableMessages).toEqual(1);
+
+      store.dispatch(actions.filterTextSet("MyNicePrefix:"));
+      messages = getVisibleMessages(store.getState());
+      expect(messages.length - numUnfilterableMessages).toEqual(1);
+    });
+
     it("restores all messages once text is cleared", () => {
       store.dispatch(actions.filterTextSet("danger"));
       store.dispatch(actions.filterTextSet(""));
 
       let messages = getVisibleMessages(store.getState());
       expect(messages.length).toEqual(numMessages);
     });
   });

--- a/devtools/client/webconsole/new-console-output/types.js
+++ b/devtools/client/webconsole/new-console-output/types.js
@@ -38,16 +38,17 @@ exports.ConsoleMessage = function (props
     repeatId: null,
     stacktrace: null,
     frame: null,
     groupId: null,
     exceptionDocURL: null,
     userProvidedStyles: null,
     notes: null,
     indent: 0,
+    prefix: "",
   }, props);
 };
 
 exports.NetworkEventMessage = function (props) {
   return Object.assign({
     id: null,
     actor: null,
     level: MESSAGE_LEVEL.LOG,

--- a/devtools/client/webconsole/new-console-output/utils/messages.js
+++ b/devtools/client/webconsole/new-console-output/utils/messages.js
@@ -15,17 +15,16 @@ const {
   MESSAGE_LEVEL,
 } = require("../constants");
 const {
   ConsoleMessage,
   NetworkEventMessage,
 } = require("../types");
 
 function prepareMessage(packet, idGenerator) {
-  // This packet is already in the expected packet structure. Simply return.
   if (!packet.source) {
     packet = transformPacket(packet);
   }
 
   if (packet.allowRepeating) {
     packet.repeatId = getRepeatId(packet);
   }
   packet.id = idGenerator.getNextId(packet);
@@ -162,16 +161,17 @@ function transformConsoleAPICallPacket(p
     type,
     level,
     parameters,
     messageText,
     stacktrace: message.stacktrace ? message.stacktrace : null,
     frame,
     timeStamp: message.timeStamp,
     userProvidedStyles: message.styles,
+    prefix: message.prefix,
   });
 }
 
 function transformNavigationMessagePacket(packet) {
   let { message } = packet;
   return new ConsoleMessage({
     source: MESSAGE_SOURCE.CONSOLE_API,
     type: MESSAGE_TYPE.LOG,