--- a/devtools/client/netmonitor/src/assets/styles/RequestList.css
+++ b/devtools/client/netmonitor/src/assets/styles/RequestList.css
@@ -296,25 +296,16 @@
 .requests-list-file {
   width: 22%;
 }
 
 .requests-list-file.requests-list-column {
   text-align: start;
 }
 
-.requests-list-icon {
-  background: transparent;
-  width: 15px;
-  height: 15px;
-  margin: 0 4px;
-  outline: 1px solid var(--table-splitter-color);
-  vertical-align: top;
-}
-
 /* Protocol column */
 
 .requests-list-protocol {
   width: 8%;
 }
 
 /* Cookies column */
 

--- a/devtools/client/netmonitor/src/components/RequestListColumnFile.js
+++ b/devtools/client/netmonitor/src/components/RequestListColumnFile.js
@@ -6,50 +6,42 @@
 
 const {
   Component,
   DOM,
   PropTypes,
 } = require("devtools/client/shared/vendor/react");
 const { propertiesEqual } = require("../utils/request-utils");
 
-const { div, img } = DOM;
+const { div } = DOM;
 
 const UPDATED_FILE_PROPS = [
-  "responseContentDataUri",
   "urlDetails",
 ];
 
 class RequestListColumnFile extends Component {
   static get propTypes() {
     return {
       item: PropTypes.object.isRequired,
-      onThumbnailMouseDown: PropTypes.func.isRequired,
     };
   }
 
   shouldComponentUpdate(nextProps) {
     return !propertiesEqual(UPDATED_FILE_PROPS, this.props.item, nextProps.item);
   }
 
   render() {
     let {
-      item: { responseContentDataUri, urlDetails },
-      onThumbnailMouseDown
+      item: { urlDetails },
     } = this.props;
 
     return (
       div({
         className: "requests-list-column requests-list-file",
         title: urlDetails.unicodeUrl,
       },
-        img({
-          className: "requests-list-icon",
-          src: responseContentDataUri,
-          onMouseDown: onThumbnailMouseDown,
-        }),
         urlDetails.baseNameWithQuery
       )
     );
   }
 }
 
 module.exports = RequestListColumnFile;

--- a/devtools/client/netmonitor/src/components/RequestListContent.js
+++ b/devtools/client/netmonitor/src/components/RequestListContent.js
@@ -42,17 +42,16 @@ class RequestListContent extends Compone
       dispatch: PropTypes.func.isRequired,
       displayedRequests: PropTypes.object.isRequired,
       firstRequestStartedMillis: PropTypes.number.isRequired,
       fromCache: PropTypes.bool,
       onCauseBadgeMouseDown: PropTypes.func.isRequired,
       onItemMouseDown: PropTypes.func.isRequired,
       onSecurityIconMouseDown: PropTypes.func.isRequired,
       onSelectDelta: PropTypes.func.isRequired,
-      onThumbnailMouseDown: PropTypes.func.isRequired,
       onWaterfallMouseDown: PropTypes.func.isRequired,
       scale: PropTypes.number,
       selectedRequestId: PropTypes.string,
     };
   }
 
   constructor(props) {
     super(props);
@@ -144,17 +143,17 @@ class RequestListContent extends Compone
       return false;
     }
     let requestItem = this.props.displayedRequests.find(r => r.id == itemId);
     if (!requestItem) {
       return false;
     }
 
     let { connector } = this.props;
-    if (requestItem.responseContent && target.closest(".requests-list-icon")) {
+    if (target.closest(".requests-list-file")) {
       return setTooltipImageContent(connector, tooltip, itemEl, requestItem);
     }
 
     return false;
   }
 
   /**
    * Scroll listener for the requests menu view.
@@ -217,17 +216,16 @@ class RequestListContent extends Compone
   render() {
     const {
       columns,
       displayedRequests,
       firstRequestStartedMillis,
       onCauseBadgeMouseDown,
       onItemMouseDown,
       onSecurityIconMouseDown,
-      onThumbnailMouseDown,
       onWaterfallMouseDown,
       scale,
       selectedRequestId,
     } = this.props;
 
     return (
       div({ className: "requests-list-wrapper"},
         div({ className: "requests-list-table"},
@@ -247,17 +245,16 @@ class RequestListContent extends Compone
               index,
               isSelected: item.id === selectedRequestId,
               key: item.id,
               onContextMenu: this.onContextMenu,
               onFocusedNodeChange: this.onFocusedNodeChange,
               onMouseDown: () => onItemMouseDown(item.id),
               onCauseBadgeMouseDown: () => onCauseBadgeMouseDown(item.cause),
               onSecurityIconMouseDown: () => onSecurityIconMouseDown(item.securityState),
-              onThumbnailMouseDown: () => onThumbnailMouseDown(),
               onWaterfallMouseDown: () => onWaterfallMouseDown(),
             }))
           )
         )
       )
     );
   }
 }
@@ -287,22 +284,15 @@ module.exports = connect(
      */
     onSecurityIconMouseDown: (securityState) => {
       if (securityState && securityState !== "insecure") {
         dispatch(Actions.selectDetailsPanelTab("security"));
       }
     },
     onSelectDelta: (delta) => dispatch(Actions.selectDelta(delta)),
     /**
-     * A handler that opens the response tab in the details view if
-     * the thumbnail is clicked.
-     */
-    onThumbnailMouseDown: () => {
-      dispatch(Actions.selectDetailsPanelTab("response"));
-    },
-    /**
      * A handler that opens the timing sidebar panel if the waterfall is clicked.
      */
     onWaterfallMouseDown: () => {
       dispatch(Actions.selectDetailsPanelTab("timings"));
     },
   }),
 )(RequestListContent);

--- a/devtools/client/netmonitor/src/components/RequestListItem.js
+++ b/devtools/client/netmonitor/src/components/RequestListItem.js
@@ -81,17 +81,16 @@ class RequestListItem extends Component 
       isSelected: PropTypes.bool.isRequired,
       firstRequestStartedMillis: PropTypes.number.isRequired,
       fromCache: PropTypes.bool,
       onCauseBadgeMouseDown: PropTypes.func.isRequired,
       onContextMenu: PropTypes.func.isRequired,
       onFocusedNodeChange: PropTypes.func,
       onMouseDown: PropTypes.func.isRequired,
       onSecurityIconMouseDown: PropTypes.func.isRequired,
-      onThumbnailMouseDown: PropTypes.func.isRequired,
       onWaterfallMouseDown: PropTypes.func.isRequired,
       waterfallWidth: PropTypes.number,
     };
   }
 
   componentDidMount() {
     if (this.props.isSelected) {
       this.refs.listItem.focus();
@@ -120,17 +119,16 @@ class RequestListItem extends Component 
       index,
       isSelected,
       firstRequestStartedMillis,
       fromCache,
       onContextMenu,
       onMouseDown,
       onCauseBadgeMouseDown,
       onSecurityIconMouseDown,
-      onThumbnailMouseDown,
       onWaterfallMouseDown,
     } = this.props;
 
     let classList = ["request-list-item", index % 2 ? "odd" : "even"];
     isSelected && classList.push("selected");
     fromCache && classList.push("fromCache");
 
     return (
@@ -139,17 +137,17 @@ class RequestListItem extends Component 
         className: classList.join(" "),
         "data-id": item.id,
         tabIndex: 0,
         onContextMenu,
         onMouseDown,
       },
         columns.get("status") && RequestListColumnStatus({ item }),
         columns.get("method") && RequestListColumnMethod({ item }),
-        columns.get("file") && RequestListColumnFile({ item, onThumbnailMouseDown }),
+        columns.get("file") && RequestListColumnFile({ item }),
         columns.get("protocol") && RequestListColumnProtocol({ item }),
         columns.get("scheme") && RequestListColumnScheme({ item }),
         columns.get("domain") && RequestListColumnDomain({ item,
                                                            onSecurityIconMouseDown }),
         columns.get("remoteip") && RequestListColumnRemoteIP({ item }),
         columns.get("cause") && RequestListColumnCause({ item, onCauseBadgeMouseDown }),
         columns.get("type") && RequestListColumnType({ item }),
         columns.get("cookies") && RequestListColumnCookies({ item }),

--- a/devtools/client/netmonitor/src/connector/chrome/response.js
+++ b/devtools/client/netmonitor/src/connector/chrome/response.js
@@ -1,16 +1,14 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
-const { formDataURI } = require("../../utils/request-utils");
-
 function ResponseInfo(id, response, content) {
   let {
     mimeType
   } = response;
   const {body, base64Encoded} = content;
   return {
     from: id,
     content: {
@@ -18,29 +16,26 @@ function ResponseInfo(id, response, cont
       text: !body ? "" : body,
       size: !body ? 0 : body.length,
       encoding: base64Encoded ? "base64" : undefined
     }
   };
 }
 
 function ResponseContent(id, response, content) {
-  const {body, base64Encoded} = content;
+  const {body} = content;
   let {mimeType, encodedDataLength} = response;
   let responseContent = ResponseInfo(id, response, content);
   let payload = Object.assign(
     {
       responseContent,
       contentSize: !body ? 0 : body.length,
       transferredSize: encodedDataLength, // TODO: verify
       mimeType: mimeType
     }, body);
-  if (mimeType.includes("image/")) {
-    payload.responseContentDataUri = formDataURI(mimeType, base64Encoded, response);
-  }
   return payload;
 }
 
 /**
  * Not support on current version.
  * unstable method: Security
  * cause: https://chromedevtools.github.io/devtools-protocol/tot/Security/
  */

--- a/devtools/client/netmonitor/src/connector/firefox-data-provider.js
+++ b/devtools/client/netmonitor/src/connector/firefox-data-provider.js
@@ -4,17 +4,16 @@
 /* eslint-disable block-scoped-var */
 
 "use strict";
 
 const { EVENTS } = require("../constants");
 const { CurlUtils } = require("devtools/client/shared/curl");
 const {
   fetchHeaders,
-  formDataURI,
 } = require("../utils/request-utils");
 
 /**
  * This object is responsible for fetching additional HTTP
  * data from the backend over RDP protocol.
  *
  * The object also keeps track of RDP requests in-progress,
  * so it's possible to determine whether all has been fetched
@@ -123,23 +122,18 @@ class FirefoxDataProvider {
     this.pushRequestToQueue(id, payload);
 
     return payload;
   }
 
   async fetchResponseContent(mimeType, responseContent) {
     let payload = {};
     if (mimeType && responseContent && responseContent.content) {
-      let { encoding, text } = responseContent.content;
+      let { text } = responseContent.content;
       let response = await this.getLongString(text);
-
-      if (mimeType.includes("image/")) {
-        payload.responseContentDataUri = formDataURI(mimeType, encoding, response);
-      }
-
       responseContent.content.text = response;
       payload.responseContent = responseContent;
     }
     return payload;
   }
 
   async fetchRequestHeaders(requestHeaders) {
     let payload = {};

--- a/devtools/client/netmonitor/src/reducers/requests.js
+++ b/devtools/client/netmonitor/src/reducers/requests.js
@@ -54,17 +54,16 @@ const Request = I.Record({
   requestHeaders: undefined,
   requestHeadersFromUploadStream: undefined,
   requestCookies: undefined,
   requestPostData: undefined,
   responseHeaders: undefined,
   responseCookies: undefined,
   responseContent: undefined,
   responseContentAvailable: false,
-  responseContentDataUri: undefined,
   formDataSections: undefined,
 });
 
 const Requests = I.Record({
   // The collection of requests (keyed by id)
   requests: I.Map(),
   // Selection state
   selectedId: null,

--- a/devtools/client/netmonitor/src/request-list-tooltip.js
+++ b/devtools/client/netmonitor/src/request-list-tooltip.js
@@ -8,27 +8,28 @@ const {
   setImageTooltip,
   getImageDimensions,
 } = require("devtools/client/shared/widgets/tooltip/ImageTooltipHelper");
 const { formDataURI } = require("./utils/request-utils");
 
 const REQUESTS_TOOLTIP_IMAGE_MAX_DIM = 400; // px
 
 async function setTooltipImageContent(connector, tooltip, itemEl, requestItem) {
-  let { mimeType, text, encoding } = requestItem.responseContent.content;
+  let { mimeType } = requestItem;
 
   if (!mimeType || !mimeType.includes("image/")) {
     return false;
   }
 
-  let string = await connector.getLongString(text);
-  let src = formDataURI(mimeType, encoding, string);
+  let responseContent = await connector.requestData(requestItem.id, "responseContent");
+  let { encoding, text } = responseContent.content;
+  let src = formDataURI(mimeType, encoding, text);
   let maxDim = REQUESTS_TOOLTIP_IMAGE_MAX_DIM;
   let { naturalWidth, naturalHeight } = await getImageDimensions(tooltip.doc, src);
   let options = { maxDim, naturalWidth, naturalHeight };
   setImageTooltip(tooltip, tooltip.doc, src, options);
 
-  return itemEl.querySelector(".requests-list-icon");
+  return itemEl.querySelector(".requests-list-file");
 }
 
 module.exports = {
   setTooltipImageContent,
 };

--- a/devtools/client/netmonitor/test/browser.ini
+++ b/devtools/client/netmonitor/test/browser.ini
@@ -117,17 +117,16 @@ skip-if = (os == 'linux' && debug && bit
 [browser_net_filter-02.js]
 [browser_net_filter-03.js]
 [browser_net_filter-04.js]
 [browser_net_filter-autocomplete.js]
 [browser_net_filter-flags.js]
 [browser_net_footer-summary.js]
 [browser_net_headers-alignment.js]
 [browser_net_headers_sorted.js]
-[browser_net_icon-preview.js]
 [browser_net_image-tooltip.js]
 [browser_net_json-b64.js]
 [browser_net_json-null.js]
 [browser_net_json-long.js]
 [browser_net_json-malformed.js]
 [browser_net_json_custom_mime.js]
 [browser_net_json_text_mime.js]
 [browser_net_jsonp.js]
@@ -171,14 +170,13 @@ skip-if = true # Bug 1258809
 [browser_net_simple-request.js]
 [browser_net_sort-01.js]
 [browser_net_sort-02.js]
 [browser_net_statistics-01.js]
 [browser_net_statistics-02.js]
 [browser_net_status-codes.js]
 [browser_net_streaming-response.js]
 [browser_net_throttle.js]
-[browser_net_thumbnail-click.js]
 [browser_net_timeline_ticks.js]
 skip-if = true # TODO: fix the test
 [browser_net_timing-division.js]
 [browser_net_truncate.js]
 [browser_net_waterfall-click.js]

deleted file mode 100644
--- a/devtools/client/netmonitor/test/browser_net_icon-preview.js
+++ /dev/null
@@ -1,68 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-"use strict";
-
-/**
- * Tests if image responses show a thumbnail in the requests menu.
- */
-
-add_task(function* () {
-  let { tab, monitor } = yield initNetMonitor(CONTENT_TYPE_WITHOUT_CACHE_URL);
-  const SELECTOR = ".requests-list-icon[src]";
-  info("Starting test... ");
-
-  let { document, store, windowRequire, connector } = monitor.panelWin;
-  let Actions = windowRequire("devtools/client/netmonitor/src/actions/index");
-  let { triggerActivity } = connector;
-  let { ACTIVITY_TYPE } = windowRequire("devtools/client/netmonitor/src/constants");
-
-  store.dispatch(Actions.batchEnable(false));
-
-  let wait = waitForNetworkEvents(monitor, CONTENT_TYPE_WITHOUT_CACHE_REQUESTS);
-  yield performRequests();
-  yield wait;
-  yield waitUntil(() => !!document.querySelector(SELECTOR));
-
-  info("Checking the image thumbnail when all items are shown.");
-  checkImageThumbnail();
-
-  store.dispatch(Actions.sortBy("contentSize"));
-  info("Checking the image thumbnail when all items are sorted.");
-  checkImageThumbnail();
-
-  store.dispatch(Actions.toggleRequestFilterType("images"));
-  info("Checking the image thumbnail when only images are shown.");
-  checkImageThumbnail();
-
-  info("Reloading the debuggee and performing all requests again...");
-  wait = waitForNetworkEvents(monitor, CONTENT_TYPE_WITHOUT_CACHE_REQUESTS);
-  yield reloadAndPerformRequests();
-  yield wait;
-  yield waitUntil(() => !!document.querySelector(SELECTOR));
-
-  info("Checking the image thumbnail after a reload.");
-  checkImageThumbnail();
-
-  yield teardown(monitor);
-
-  function performRequests() {
-    return ContentTask.spawn(tab.linkedBrowser, {}, function* () {
-      content.wrappedJSObject.performRequests();
-    });
-  }
-
-  function* reloadAndPerformRequests() {
-    yield triggerActivity(ACTIVITY_TYPE.RELOAD.WITH_CACHE_ENABLED);
-    yield performRequests();
-  }
-
-  function checkImageThumbnail() {
-    is(document.querySelectorAll(SELECTOR).length, 1,
-      "There should be only one image request with a thumbnail displayed.");
-    is(document.querySelector(SELECTOR).src, TEST_IMAGE_DATA_URI,
-      "The image requests-list-icon thumbnail is displayed correctly.");
-    is(document.querySelector(SELECTOR).hidden, false,
-      "The image requests-list-icon thumbnail should not be hidden.");
-  }
-});

--- a/devtools/client/netmonitor/test/browser_net_image-tooltip.js
+++ b/devtools/client/netmonitor/test/browser_net_image-tooltip.js
@@ -6,48 +6,45 @@
 const IMAGE_TOOLTIP_URL = EXAMPLE_URL + "html_image-tooltip-test-page.html";
 const IMAGE_TOOLTIP_REQUESTS = 1;
 
 /**
  * Tests if image responses show a popup in the requests menu when hovered.
  */
 add_task(function* test() {
   let { tab, monitor } = yield initNetMonitor(IMAGE_TOOLTIP_URL);
-  const SELECTOR = ".requests-list-icon[src]";
   info("Starting test... ");
 
   let { document, store, windowRequire, connector } = monitor.panelWin;
   let Actions = windowRequire("devtools/client/netmonitor/src/actions/index");
   let { triggerActivity } = connector;
   let { ACTIVITY_TYPE } = windowRequire("devtools/client/netmonitor/src/constants");
   let toolboxDoc = monitor.panelWin.parent.document;
 
   store.dispatch(Actions.batchEnable(false));
 
   let onEvents = waitForNetworkEvents(monitor, IMAGE_TOOLTIP_REQUESTS);
   yield performRequests();
   yield onEvents;
-  yield waitUntil(() => !!document.querySelector(SELECTOR));
 
   info("Checking the image thumbnail after a few requests were made...");
   yield showTooltipAndVerify(document.querySelectorAll(".request-list-item")[0]);
 
   // Hide tooltip before next test, to avoid the situation that tooltip covers
   // the icon for the request of the next test.
   info("Checking the image thumbnail gets hidden...");
   yield hideTooltipAndVerify(document.querySelectorAll(".request-list-item")[0]);
 
   // +1 extra document reload
   onEvents = waitForNetworkEvents(monitor, IMAGE_TOOLTIP_REQUESTS + 1);
 
   info("Reloading the debuggee and performing all requests again...");
   yield triggerActivity(ACTIVITY_TYPE.RELOAD.WITH_CACHE_ENABLED);
   yield performRequests();
   yield onEvents;
-  yield waitUntil(() => !!document.querySelector(SELECTOR));
 
   info("Checking the image thumbnail after a reload.");
   yield showTooltipAndVerify(document.querySelectorAll(".request-list-item")[1]);
 
   info("Checking if the image thumbnail is hidden when mouse leaves the menu widget");
   let requestsListContents = document.querySelector(".requests-list-contents");
   EventUtils.synthesizeMouse(requestsListContents, 0, 0, { type: "mousemove" },
                              monitor.panelWin);
@@ -61,17 +58,17 @@ add_task(function* test() {
     });
   }
 
   /**
    * Show a tooltip on the {target} and verify that it was displayed
    * with the expected content.
    */
   function* showTooltipAndVerify(target) {
-    let anchor = target.querySelector(".requests-list-icon");
+    let anchor = target.querySelector(".requests-list-file");
     yield showTooltipOn(anchor);
 
     info("Tooltip was successfully opened for the image request.");
     is(toolboxDoc.querySelector(".tooltip-panel img").src, TEST_IMAGE_DATA_URI,
       "The tooltip's image content is displayed correctly.");
   }
 
   /**

deleted file mode 100644
--- a/devtools/client/netmonitor/test/browser_net_thumbnail-click.js
+++ /dev/null
@@ -1,40 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
-   http://creativecommons.org/publicdomain/zero/1.0/ */
-
-"use strict";
-
-/**
- * Test that clicking on the file thumbnail opens the response details tab.
- */
-
-add_task(function* () {
-  let { tab, monitor } = yield initNetMonitor(CONTENT_TYPE_WITHOUT_CACHE_URL);
-  let { document } = monitor.panelWin;
-
-  yield performRequestsAndWait();
-
-  let wait = waitForDOM(document, "#response-panel");
-
-  let request = document.querySelectorAll(".request-list-item")[5];
-  let icon = request.querySelector(".requests-list-icon");
-
-  info("Clicking thumbnail of the sixth request.");
-  EventUtils.synthesizeMouseAtCenter(icon, {}, monitor.panelWin);
-
-  yield wait;
-
-  ok(document.querySelector("#response-tab[aria-selected=true]"),
-     "Response tab is selected.");
-  ok(document.querySelector(".response-image-box"),
-     "Response image preview is shown.");
-
-  yield teardown(monitor);
-
-  function* performRequestsAndWait() {
-    let onAllEvents = waitForNetworkEvents(monitor, CONTENT_TYPE_WITHOUT_CACHE_REQUESTS);
-    yield ContentTask.spawn(tab.linkedBrowser, {}, function* () {
-      content.wrappedJSObject.performRequests();
-    });
-    yield onAllEvents;
-  }
-});