diff --git a/browser/components/extensions/test/browser/browser-common.ini b/browser/components/extensions/test/browser/browser-common.ini
--- a/browser/components/extensions/test/browser/browser-common.ini
+++ b/browser/components/extensions/test/browser/browser-common.ini
@@ -62,16 +62,17 @@ skip-if = os == 'win' && !debug # Bug 13
 [browser_ext_contextMenus_urlPatterns.js]
 [browser_ext_currentWindow.js]
 [browser_ext_devtools_inspectedWindow.js]
 [browser_ext_devtools_inspectedWindow_eval_bindings.js]
 [browser_ext_devtools_inspectedWindow_reload.js]
 [browser_ext_devtools_network.js]
 [browser_ext_devtools_page.js]
 [browser_ext_devtools_panel.js]
+[browser_ext_find.js]
 [browser_ext_geckoProfiler_symbolicate.js]
 [browser_ext_getViews.js]
 [browser_ext_identity_indication.js]
 [browser_ext_incognito_views.js]
 [browser_ext_incognito_popup.js]
 [browser_ext_lastError.js]
 [browser_ext_menus.js]
 [browser_ext_omnibox.js]
diff --git a/browser/components/extensions/test/browser/browser_ext_find.js b/browser/components/extensions/test/browser/browser_ext_find.js
new file mode 100644
--- /dev/null
+++ b/browser/components/extensions/test/browser/browser_ext_find.js
@@ -0,0 +1,139 @@
+"use strict";
+
+function frameScript() {
+  function getSelectedText() {
+    var frame = this.content.frames[0].frames[1];
+    var Ci = Components.interfaces;
+    var docShell = frame.QueryInterface(Ci.nsIInterfaceRequestor)
+                        .getInterface(Ci.nsIWebNavigation)
+                        .QueryInterface(Ci.nsIDocShell);
+    var controller = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
+                             .getInterface(Ci.nsISelectionDisplay)
+                             .QueryInterface(Ci.nsISelectionController);
+    var selection = controller.getSelection(controller.SELECTION_FIND);
+    var range = selection.getRangeAt(0);
+    var r1 = frame.parent.frameElement.getBoundingClientRect();
+    var r2 = frame.frameElement.getBoundingClientRect();
+    var r3 = range.getBoundingClientRect();
+    var rect = { top: (r1.top + r2.top + r3.top), left: (r1.left + r2.left + r3.left) };
+    this.sendAsyncMessage("test:find:selectionTest", { text: selection.toString(), rect });
+  };
+  getSelectedText();
+}
+
+function waitForMessage(browser, topic) {
+  let mm = browser.messageManager;
+  return new Promise(resolve => {
+    mm.addMessageListener(topic, function messageListener(message) {
+      mm.removeMessageListener(topic, messageListener);
+      resolve(message);
+    });
+  });
+}
+
+add_task(async function testDuplicatePinnedTab() {
+  async function background() {
+    function awaitLoad(tabId) {
+      return new Promise(resolve => {
+        browser.tabs.onUpdated.addListener(function listener(tabId_, changed, tab) {
+          if (tabId == tabId_ && changed.status == "complete") {
+            browser.tabs.onUpdated.removeListener(listener);
+            resolve();
+          }
+        });
+      });
+    }
+
+    let url = "http://example.com/browser/browser/components/extensions/test/browser/file_find_frames.html";
+    let tab = await browser.tabs.update({url});
+    await awaitLoad(tab.id);
+
+    let data = await browser.find.search("banana", { includeRangeData: true });
+    let rangeData = data.rangeData
+
+    browser.test.log("Test that `data.count` is the expected value.");
+    browser.test.assertEq(6, data.count, "The value returned from `data.count`");
+
+    browser.test.log("Test that `rangeData` has the proper number of values.");
+    browser.test.assertEq(6, rangeData.length, "The number of values held in `rangeData`");
+
+    browser.test.log("Test that the text found in the top window and nested frames corresponds to the proper position.");
+    let terms = ["Banana", "bAnana", "baNana", "banAna", "banaNa", "bananA"];
+    for (let i = 0; i < terms.length; i++) {
+      browser.test.assertEq(terms[i], rangeData[i].text, `The text at range position ${i}:`);
+    }
+
+    browser.test.log("Test that case sensitive match works properly.");
+    data = await browser.find.search("baNana", { caseSensitive: true, includeRangeData: true });
+    browser.test.assertEq(1, data.count, "The number of matches found:");
+    browser.test.assertEq("baNana", data.rangeData[0].text, "The text found:");
+
+    browser.test.log("Test that case insensitive match works properly.");
+    data = await browser.find.search("banana", { caseSensitive: false });
+    browser.test.assertEq(6, data.count, "The number of matches found:");
+
+    browser.test.log("Test that entire word match works properly.");
+    data = await browser.find.search("banana", { entireWord: true });
+    browser.test.assertEq(4, data.count, "The number of matches found, should skip 2 matches, \"banaNaland\" amd \"bananAland\":");
+
+    browser.test.log("Test that `rangeData` is not returned if `includeRangeData` is false.");
+    data = await browser.find.search("banana", { caseSensitive: false, includeRangeData: false });
+    browser.test.assertEq(false, !!data.rangeData, "The boolean cast value of `rangeData`:");
+
+    browser.test.log("Test that `rectData` is not returned if `includeRectData` is false.");
+    data = await browser.find.search("banana", { caseSensitive: false, includeRectData: false });
+    browser.test.assertEq(false, !!data.rectData, "The boolean cast value of `rectData`:");
+
+    browser.test.log("Test that text spanning multiple inline elements is found.");
+    data = await browser.find.search("fruitcake");
+    browser.test.assertEq(1, data.count, "The number of matches found:");
+
+    browser.test.log("Test that text spanning multiple block elements is not found.");
+    data = await browser.find.search("angelfood");
+    browser.test.assertEq(0, data.count, "The number of matches found:");
+
+    browser.test.log("Test that `highlightResults` returns proper status code.");
+    await browser.find.search("banana");
+
+    let result = await browser.find.highlightResults({ rangeIndex: 0 });
+    browser.test.assertEq(1, result.status, "The status code is the proper value:");
+
+    result = await browser.find.highlightResults({ rangeIndex: 6 });
+    browser.test.assertEq(2, result.status, "The status code is the proper value:");
+
+    data = await browser.find.search("xyz");
+    result = await browser.find.highlightResults({ rangeIndex: 0 });
+    browser.test.assertEq(3, result.status, "The status code is the proper value:");
+
+    data = await browser.find.search("banana", { includeRectData: true });
+    result = await browser.find.highlightResults({ rangeIndex: 5 });
+
+    browser.test.sendMessage("test:find:WebExtensionFinished", data.rectData);
+  }
+
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      "permissions": ["find", "tabs"],
+    },
+    background,
+  });
+
+  await extension.startup();
+  let rectData = await extension.awaitMessage("test:find:WebExtensionFinished");
+  let { top, left } = rectData[5].rectsAndTexts.rectList[0];
+  await extension.unload();
+
+  let browser = gBrowser.selectedBrowser;
+
+  let frameScriptUrl = `data:,(${frameScript})()`;
+  browser.messageManager.loadFrameScript(frameScriptUrl, false);
+  let message = await waitForMessage(browser, "test:find:selectionTest");
+
+  info("Test that text was highlighted properly.");
+  is (message.data.text, "bananA", `The text that was highlighted: - Expected: bananA, Actual: ${message.data.text}`);
+
+  info("Test that rectangle data returned from the search matches the highlighted result.");
+  is (message.data.rect.top, top, `rect.top: - Expected: ${message.data.rect.top}, Actual: ${top}`);
+  is (message.data.rect.left, left, `rect.left: - Expected: ${message.data.rect.left}, Actual: ${left}`);
+});
+
diff --git a/browser/components/extensions/test/browser/file_find_frames.html b/browser/components/extensions/test/browser/file_find_frames.html
new file mode 100644
--- /dev/null
+++ b/browser/components/extensions/test/browser/file_find_frames.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+<body>
+
+<p>Banana 0</p>
+<iframe src="data:text/html,<p>baNana 2</p>
+                            <iframe src='data:text/html,banaNaland 4' height='50' width='100%'></iframe>
+                            <iframe src='data:text/html,bananAland 5' height='50' width='100%'></iframe>
+                            <p>banAna 3</p>" height="250" width="100%"></iframe>
+<p>bAnana 1</p>
+<p><b>fru</b>it<i><b>ca</b>ke</i></p>
+<p>ang<div>elf</div>ood</p>
+</body>
+</html>
+