--- a/devtools/client/webconsole/test/fixtures/stub-generators/head.js
+++ b/devtools/client/webconsole/test/fixtures/stub-generators/head.js
@@ -273,18 +273,18 @@ function formatFile(stubs, type) {
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { ${type} } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 ${stubs.preparedMessages.join("\n\n")}
 
 ${stubs.packets.join("\n\n")}
 
 module.exports = {
   stubPreparedMessages,
   stubPackets,
 };

--- a/devtools/client/webconsole/test/fixtures/stubs/consoleApi.js
+++ b/devtools/client/webconsole/test/fixtures/stubs/consoleApi.js
@@ -6,18 +6,18 @@
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { ConsoleMessage } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 stubPreparedMessages.set(`console.log('foobar', 'test')`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "console-api",
   "timeStamp": 1502884924471,
   "type": "log",
   "helperType": null,
   "level": "log",

--- a/devtools/client/webconsole/test/fixtures/stubs/cssMessage.js
+++ b/devtools/client/webconsole/test/fixtures/stubs/cssMessage.js
@@ -6,18 +6,18 @@
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { ConsoleMessage } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 stubPreparedMessages.set(`Unknown property ‘such-unknown-property’.  Declaration dropped.`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "css",
   "timeStamp": 1479159920406,
   "type": "log",
   "helperType": null,
   "level": "warn",

--- a/devtools/client/webconsole/test/fixtures/stubs/evaluationResult.js
+++ b/devtools/client/webconsole/test/fixtures/stubs/evaluationResult.js
@@ -6,18 +6,18 @@
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { ConsoleMessage } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 stubPreparedMessages.set(`new Date(0)`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1479159921364,
   "type": "result",
   "helperType": null,
   "level": "log",

--- a/devtools/client/webconsole/test/fixtures/stubs/networkEvent.js
+++ b/devtools/client/webconsole/test/fixtures/stubs/networkEvent.js
@@ -6,18 +6,18 @@
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { NetworkEventMessage } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 stubPreparedMessages.set("GET request", new NetworkEventMessage({
   "id": "1",
   "actor": "server1.conn0.child1/netEvent30",
   "level": "log",
   "isXHR": false,
   "request": {
     "url": "http://example.com/browser/devtools/client/webconsole/test/fixtures/stub-generators/inexistent.html",
     "method": "GET"

--- a/devtools/client/webconsole/test/fixtures/stubs/pageError.js
+++ b/devtools/client/webconsole/test/fixtures/stubs/pageError.js
@@ -6,18 +6,18 @@
 
 /*
  * THIS FILE IS AUTOGENERATED. DO NOT MODIFY BY HAND. RUN TESTS IN FIXTURES/ TO UPDATE.
  */
 
 const { ConsoleMessage } =
   require("devtools/client/webconsole/types");
 
-let stubPreparedMessages = new Map();
-let stubPackets = new Map();
+const stubPreparedMessages = new Map();
+const stubPackets = new Map();
 stubPreparedMessages.set(`ReferenceError: asdf is not defined`, new ConsoleMessage({
   "id": "1",
   "allowRepeating": true,
   "source": "javascript",
   "timeStamp": 1476573167137,
   "type": "log",
   "helperType": null,
   "level": "error",