Bug 1491417 - Fix typo in browser_popup_mouseover.js r=adw

Differential Revision: https://phabricator.services.mozilla.com/D5896

--HG--
extra : moz-landing-system : lando

toolkit/components/satchel/test/browser/browser_popup_mouseover.js

@@ -35,7 +35,7 @@ add_task(async function test() {
     is(listItemElems.length, mockHistory.length, "ensure result length");
     is(itemsBox.mousedOverIndex, -1, "mousedOverIndex should be -1");
 
-    // navigate to the firt item
+    // navigate to the first item
     await BrowserTestUtils.synthesizeKey("VK_DOWN", {}, browser);
     is(autoCompletePopup.selectedIndex, 0, "selectedIndex should be 0");