--- a/devtools/client/inspector/grids/components/Grid.js
+++ b/devtools/client/inspector/grids/components/Grid.js
@@ -18,17 +18,16 @@ module.exports = createClass({
 
   displayName: "Grid",
 
   propTypes: {
     getSwatchColorPickerTooltip: PropTypes.func.isRequired,
     grids: PropTypes.arrayOf(PropTypes.shape(Types.grid)).isRequired,
     highlighterSettings: PropTypes.shape(Types.highlighterSettings).isRequired,
     setSelectedNode: PropTypes.func.isRequired,
-    showGridOutline: PropTypes.bool.isRequired,
     onHideBoxModelHighlighter: PropTypes.func.isRequired,
     onSetGridOverlayColor: PropTypes.func.isRequired,
     onShowBoxModelHighlighterForNode: PropTypes.func.isRequired,
     onShowGridAreaHighlight: PropTypes.func.isRequired,
     onShowGridCellHighlight: PropTypes.func.isRequired,
     onShowGridLineNamesHighlight: PropTypes.func.isRequired,
     onToggleGridHighlighter: PropTypes.func.isRequired,
     onToggleShowGridAreas: PropTypes.func.isRequired,
@@ -39,17 +38,16 @@ module.exports = createClass({
   mixins: [ addons.PureRenderMixin ],
 
   render() {
     let {
       getSwatchColorPickerTooltip,
       grids,
       highlighterSettings,
       setSelectedNode,
-      showGridOutline,
       onHideBoxModelHighlighter,
       onSetGridOverlayColor,
       onShowBoxModelHighlighterForNode,
       onShowGridAreaHighlight,
       onShowGridCellHighlight,
       onToggleShowGridAreas,
       onToggleGridHighlighter,
       onToggleShowGridLineNumbers,
@@ -76,24 +74,21 @@ module.exports = createClass({
           }),
           GridDisplaySettings({
             highlighterSettings,
             onToggleShowGridAreas,
             onToggleShowGridLineNumbers,
             onToggleShowInfiniteLines,
           })
         ),
-        showGridOutline ?
-          GridOutline({
-            grids,
-            onShowGridAreaHighlight,
-            onShowGridCellHighlight,
-          })
-          :
-          null
+        GridOutline({
+          grids,
+          onShowGridAreaHighlight,
+          onShowGridCellHighlight,
+        })
       )
       :
       dom.div(
         {
           className: "layout-no-grids",
         },
         getStr("layout.noGridsOnThisPage")
       );

--- a/devtools/client/inspector/grids/components/GridOutline.js
+++ b/devtools/client/inspector/grids/components/GridOutline.js
@@ -292,16 +292,17 @@ module.exports = createClass({
     );
   },
 
   renderGridOutline(grid) {
     let { color } = grid;
 
     return dom.g(
       {
+        id: "grid-cell-group",
         "className": "grid-cell-group",
         "data-grid-line-color": color,
         "style": { color }
       },
       this.renderGrid(grid)
     );
   },
 
@@ -324,33 +325,35 @@ module.exports = createClass({
       selectedGrid,
       showOutline,
       width,
     } = this.state;
 
     return showOutline ?
       dom.svg(
         {
+          id: "grid-outline",
           width: "100%",
           height: this.getHeight(),
           viewBox: `${TRANSLATE_X} ${TRANSLATE_Y} ${width} ${height}`,
         },
         this.renderGridOutline(selectedGrid)
       )
       :
       this.renderCannotShowOutlineText();
   },
 
   render() {
     const { selectedGrid } = this.state;
 
     return selectedGrid ?
       dom.div(
         {
-          className: "grid-outline",
+          id: "grid-outline-container",
+          className: "grid-outline-container",
         },
         this.renderOutline()
       )
       :
       null;
   },
 
 });

--- a/devtools/client/inspector/grids/test/browser.ini
+++ b/devtools/client/inspector/grids/test/browser.ini
@@ -19,9 +19,13 @@ support-files =
 [browser_grids_grid-list-color-picker-on-ESC.js]
 [browser_grids_grid-list-color-picker-on-RETURN.js]
 [browser_grids_grid-list-element-rep.js]
 [browser_grids_grid-list-no-grids.js]
 [browser_grids_grid-list-on-mutation-element-added.js]
 [browser_grids_grid-list-on-mutation-element-removed.js]
 [browser_grids_grid-list-toggle-multiple-grids.js]
 [browser_grids_grid-list-toggle-single-grid.js]
+[browser_grids_grid-outline-cannot-show-outline.js]
+[browser_grids_grid-outline-highlight-areas.js]
+[browser_grids_grid-outline-highlight-cell.js]
+[browser_grids_grid-outline-selected-grid.js]
 [browser_grids_highlighter-setting-rules-grid-toggle.js]

new file mode 100644
--- /dev/null
+++ b/devtools/client/inspector/grids/test/browser_grids_grid-outline-cannot-show-outline.js
@@ -0,0 +1,52 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that grid outline does not show when cells are too small to be drawn and that
+// "Cannot show outline for this grid." message is displayed.
+
+const TEST_URI = `
+  <style type='text/css'>
+    #grid {
+      display: grid;
+      grid-template-columns: 2px;
+    }
+    .cell {
+      grid-template-columns: 2px;
+    }
+  </style>
+  <div id="grid">
+    <div id="cellA" className="cell">cell A</div>
+    <div id="cellB" className="cell">cell B</div>
+  </div>
+`;
+
+add_task(function* () {
+  yield addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+
+  let { inspector, gridInspector } = yield openLayoutView();
+  let { document: doc } = gridInspector;
+  let { highlighters, store } = inspector;
+
+  yield selectNode("#grid", inspector);
+  let outline = doc.getElementById("grid-outline-container");
+  let gridList = doc.querySelector("#grid-list");
+  let checkbox = gridList.children[0].querySelector("input");
+
+  info("Toggling ON the CSS grid highlighter from the layout panel.");
+  let onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  let onCheckboxChange = waitUntilState(store, state =>
+    state.grids.length == 1 &&
+    state.grids[0].highlighted);
+  checkbox.click();
+  yield onHighlighterShown;
+  yield onCheckboxChange;
+
+  let cannotShowGridOutline = doc.querySelector(".grid-outline-text");
+
+  info("Checking the grid outline is not rendered and an appropriate message is shown.");
+  ok(!outline, "Outline component is not shown.");
+  ok(cannotShowGridOutline,
+    "The message 'Cannot show outline for this grid' is displayed.");
+});

new file mode 100644
--- /dev/null
+++ b/devtools/client/inspector/grids/test/browser_grids_grid-outline-highlight-areas.js
@@ -0,0 +1,77 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the grid area and cell are highlighted when mouseovering a grid area in the
+// grid outline.
+
+const TEST_URI = `
+  <style type='text/css'>
+    #grid {
+      display: grid;
+      height: 100px;
+      grid-template-areas:
+        "header"
+        "footer";
+    }
+    .top {
+      grid-area: header;
+    }
+    .bottom {
+      grid-area: footer;
+    }
+  </style>
+  <div id="grid">
+    <div id="cella" className="top">Cell A</div>
+    <div id="cellb" className="bottom">Cell B</div>
+  </div>
+`;
+
+add_task(function* () {
+  yield addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+
+  let { inspector, gridInspector } = yield openLayoutView();
+  let { document: doc } = gridInspector;
+  let { highlighters, store } = inspector;
+
+  yield selectNode("#grid", inspector);
+  let gridList = doc.querySelector("#grid-list");
+  let checkbox = gridList.children[0].querySelector("input");
+
+  info("Toggling ON the CSS grid highlighter from the layout panel.");
+  let onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  let onCheckboxChange = waitUntilState(store, state =>
+    state.grids.length == 1 &&
+    state.grids[0].highlighted);
+  checkbox.click();
+  yield onHighlighterShown;
+  yield onCheckboxChange;
+
+  let gridOutline = doc.querySelector("#grid-outline");
+  let gridCellA = gridOutline.children[0].querySelectorAll(
+    "[data-grid-id='0'][data-grid-row='1'][data-grid-column='1']");
+
+  info("Scrolling into the view of the #grid-outline.");
+  gridCellA[0].scrollIntoView();
+
+  info("Hovering over grid cell A in the grid outline.");
+  let onCellAHighlight = highlighters.once("grid-highlighter-shown",
+      (event, nodeFront, options) => {
+        info("Checking the grid highlighter options for the show grid area" +
+        "and cell parameters.");
+        const { showGridCell, showGridArea } = options;
+        const { gridFragmentIndex, rowNumber, columnNumber } = showGridCell;
+
+        ok(showGridCell, "Show grid cell options are available.");
+        ok(showGridArea, "Show grid areas options are available.");
+
+        is(gridFragmentIndex, 0, "Should be the first grid fragment index.");
+        is(rowNumber, 1, "Should be the first grid row.");
+        is(columnNumber, 1, "Should be the first grid column.");
+
+        is(showGridArea, "header", "Grid area name should be 'header'.");
+      });
+  EventUtils.synthesizeMouse(gridCellA[0], 10, 5, {type: "mouseover"}, doc.defaultView);
+  yield onCellAHighlight;
+});

new file mode 100644
--- /dev/null
+++ b/devtools/client/inspector/grids/test/browser_grids_grid-outline-highlight-cell.js
@@ -0,0 +1,65 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the grid cell is highlighted when mouseovering the grid outline of a
+// grid cell.
+
+const TEST_URI = `
+  <style type='text/css'>
+    #grid {
+      display: grid;
+    }
+  </style>
+  <div id="grid">
+    <div id="cella">Cell A</div>
+    <div id="cellb">Cell B</div>
+  </div>
+`;
+
+add_task(function* () {
+  yield addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+
+  let { inspector, gridInspector } = yield openLayoutView();
+  let { document: doc } = gridInspector;
+  let { highlighters, store } = inspector;
+
+  yield selectNode("#grid", inspector);
+  let gridList = doc.querySelector("#grid-list");
+  let checkbox = gridList.children[0].querySelector("input");
+
+  info("Toggling ON the CSS grid highlighter from the layout panel.");
+  let onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  let onCheckboxChange = waitUntilState(store, state =>
+    state.grids.length == 1 &&
+    state.grids[0].highlighted);
+  checkbox.click();
+  yield onHighlighterShown;
+  yield onCheckboxChange;
+
+  let gridOutline = doc.querySelector("#grid-outline");
+  let gridCellA = gridOutline.children[0].querySelectorAll(
+    "[data-grid-id='0'][data-grid-row='1'][data-grid-column='1']");
+
+  info("Checking Grid Cell A and B have been rendered.");
+  is(gridCellA.length, 1, "Only one grid cell A should be rendered.");
+
+  info("Scrolling into the view the #grid-outline-container.");
+  gridCellA[0].scrollIntoView();
+
+  info("Hovering over grid cell A in the grid outline.");
+  let onCellAHighlight = highlighters.once("grid-highlighter-shown",
+      (event, nodeFront, options) => {
+        info("Checking show grid cell options are correct.");
+        const { showGridCell } = options;
+        const { gridFragmentIndex, rowNumber, columnNumber } = showGridCell;
+
+        ok(showGridCell, "Show grid cell options are available.");
+        is(gridFragmentIndex, 0, "Should be the first grid fragment index.");
+        is(rowNumber, 1, "Should be the first grid row.");
+        is(columnNumber, 1, "Should be the first grid column.");
+      });
+  EventUtils.synthesizeMouse(gridCellA[0], 10, 5, {type: "mouseover"}, doc.defaultView);
+  yield onCellAHighlight;
+});

new file mode 100644
--- /dev/null
+++ b/devtools/client/inspector/grids/test/browser_grids_grid-outline-selected-grid.js
@@ -0,0 +1,61 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the grid outline is shown when a grid container is selected.
+
+const TEST_URI = `
+  <style type='text/css'>
+    #grid {
+      display: grid;
+    }
+  </style>
+  <div id="grid">
+    <div id="cella">Cell A</div>
+    <div id="cellb">Cell B</div>
+    <div id="cellc">Cell C</div>
+  </div>
+`;
+
+add_task(function* () {
+  yield addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+
+  let { inspector, gridInspector } = yield openLayoutView();
+  let { document: doc } = gridInspector;
+  let { highlighters, store } = inspector;
+
+  yield selectNode("#grid", inspector);
+  let outline = doc.getElementById("grid-outline-container");
+  let gridList = doc.querySelector("#grid-list");
+  let checkbox = gridList.children[0].querySelector("input");
+
+  info("Checking the initial state of the Grid Inspector.");
+  ok(!outline, "There should be no grid outline shown.");
+
+  info("Toggling ON the CSS grid highlighter from the layout panel.");
+  let onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  let onCheckboxChange = waitUntilState(store, state =>
+    state.grids.length == 1 &&
+    state.grids[0].highlighted);
+  checkbox.click();
+  yield onHighlighterShown;
+  yield onCheckboxChange;
+
+  outline = doc.getElementById("grid-outline-container");
+  info("Checking the grid outline is shown.");
+  is(outline.childNodes.length, 1, "One grid container outline is shown.");
+
+  info("Toggling OFF the CSS grid highlighter from the layout panel.");
+  let onHighlighterHidden = highlighters.once("grid-highlighter-hidden");
+  onCheckboxChange = waitUntilState(store, state =>
+    state.grids.length == 1 &&
+    !state.grids[0].highlighted);
+  checkbox.click();
+  yield onHighlighterHidden;
+  yield onCheckboxChange;
+
+  outline = doc.getElementById("grid-outline-container");
+  info("Checking the grid outline is hidden.");
+  ok(!outline, "There should be no outline shown.");
+});

--- a/devtools/client/inspector/layout/layout.js
+++ b/devtools/client/inspector/layout/layout.js
@@ -10,18 +10,16 @@ const { createFactory, createElement } =
 const { Provider } = require("devtools/client/shared/vendor/react-redux");
 
 const App = createFactory(require("./components/App"));
 
 const { LocalizationHelper } = require("devtools/shared/l10n");
 const INSPECTOR_L10N =
   new LocalizationHelper("devtools/client/locales/inspector.properties");
 
-const SHOW_GRID_OUTLINE_PREF = "devtools.gridinspector.showGridOutline";
-
 function LayoutView(inspector, window) {
   this.document = window.document;
   this.inspector = inspector;
   this.store = inspector.store;
 
   this.init();
 }
 
@@ -60,22 +58,16 @@ LayoutView.prototype = {
       getSwatchColorPickerTooltip,
       setSelectedNode,
       /**
        * Shows the box model properties under the box model if true, otherwise, hidden by
        * default.
        */
       showBoxModelProperties: true,
 
-      /**
-       * Shows the grid outline if user preferences are set to true, otherwise, hidden by
-       * default.
-       */
-      showGridOutline: Services.prefs.getBoolPref(SHOW_GRID_OUTLINE_PREF),
-
       onHideBoxModelHighlighter,
       onSetGridOverlayColor,
       onShowBoxModelEditor,
       onShowBoxModelHighlighter,
       onShowBoxModelHighlighterForNode,
       onShowGridAreaHighlight,
       onShowGridCellHighlight,
       onShowGridLineNamesHighlight,

--- a/devtools/client/preferences/devtools.js
+++ b/devtools/client/preferences/devtools.js
@@ -69,17 +69,16 @@ pref("devtools.inspector.colorWidget.ena
 pref("devtools.fontinspector.enabled", true);
 
 // Enable the Layout View
 pref("devtools.layoutview.enabled", false);
 
 // Grid highlighter preferences
 pref("devtools.gridinspector.showGridAreas", false);
 pref("devtools.gridinspector.showGridLineNumbers", false);
-pref("devtools.gridinspector.showGridOutline", false);
 pref("devtools.gridinspector.showInfiniteLines", false);
 
 // Whether or not the box model panel is opened in the computed view
 pref("devtools.computed.boxmodel.opened", true);
 // Whether or not the box model panel is opened in the layout view
 pref("devtools.layout.boxmodel.opened", true);
 // Whether or not the grid inspector panel is opened in the layout view
 pref("devtools.layout.grid.opened", true);

--- a/devtools/client/themes/layout.css
+++ b/devtools/client/themes/layout.css
@@ -72,21 +72,21 @@
 .grid-container:first-child {
   margin-bottom: 10px;
 }
 
 /**
  * Grid Outline
  */
 
-.grid-outline {
+.grid-outline-container {
   margin: 5px 0;
 }
 
-.grid-outline svg {
+.grid-outline-container svg {
   overflow: visible;
 }
 
 .grid-outline-border {
   fill: none;
   stroke: currentColor;
   stroke-width: 0.75;
   vector-effect: non-scaling-stroke;