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diff --git a/devtools/client/inspector/grids/test/browser_grids_grid-outline-multiple-grids.js b/devtools/client/inspector/grids/test/browser_grids_grid-outline-multiple-grids.js
new file mode 100644
index 0000000000..a65cfd7528
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+++ b/devtools/client/inspector/grids/test/browser_grids_grid-outline-multiple-grids.js
@@ -0,0 +1,76 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Tests that the grid outline is not shown when more than one grid is highlighted.
+
+const TEST_URI = `
+  <style type='text/css'>
+    .grid {
+      display: grid;
+    }
+  </style>
+  <div id="grid1" class="grid">
+    <div class="cell1">cell1</div>
+    <div class="cell2">cell2</div>
+  </div>
+  <div id="grid2" class="grid">
+    <div class="cell1">cell1</div>
+    <div class="cell2">cell2</div>
+  </div>
+`;
+
+add_task(async function () {
+  await pushPref("devtools.gridinspector.maxHighlighters", 2);
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, gridInspector } = await openLayoutView();
+  const { document: doc } = gridInspector;
+  const { highlighters, store } = inspector;
+
+  await selectNode("#grid1", inspector);
+  const gridList = doc.getElementById("grid-list");
+  const checkbox1 = gridList.children[0].querySelector("input");
+  const checkbox2 = gridList.children[1].querySelector("input");
+
+  info("Toggling ON the CSS grid highlighter for #grid1.");
+  let onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  const onGridOutlineRendered = waitForDOM(doc, "#grid-cell-group rect", 2);
+  let onCheckboxChange = waitUntilState(
+    store,
+    state =>
+      state.grids.length === 2 &&
+      state.grids[0].highlighted &&
+      !state.grids[1].highlighted
+  );
+  checkbox1.click();
+  await onHighlighterShown;
+  await onCheckboxChange;
+  const elements = await onGridOutlineRendered;
+
+  info("Checking the grid outline for #grid1 is shown.");
+  ok(
+    doc.getElementById("grid-outline-container"),
+    "Grid outline container is rendered."
+  );
+  is(elements.length, 2, "Grid outline is shown.");
+
+  info("Toggling ON the CSS grid highlighter for #grid2.");
+  onHighlighterShown = highlighters.once("grid-highlighter-shown");
+  onCheckboxChange = waitUntilState(
+    store,
+    state =>
+      state.grids.length === 2 &&
+      state.grids[0].highlighted &&
+      state.grids[1].highlighted
+  );
+  checkbox2.click();
+  await onHighlighterShown;
+  await onCheckboxChange;
+
+  info("Checking the grid outline is not shown.");
+  ok(
+    !doc.getElementById("grid-outline-container"),
+    "Grid outline is not rendered."
+  );
+});