Bug 1759593 - prevent multiple actions also for modified-clicks on links, to prevent nested links causing multiple tabs to open, r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D142467

browser/actors/ClickHandlerChild.jsm

@@ -184,9 +184,9 @@ class ClickHandlerChild extends JSWindowActorChild {
       // actions here to avoid leaking clipboard content unexpectedly.
       // Note that whether the link will work actually or not does not matter
       // because in this case, user does not intent to paste clipboard content.
-      if (event.button === 1) {
-        event.preventMultipleActions();
-      }
+      // We also need to do this to prevent multiple tabs opening if there are
+      // nested link elements.
+      event.preventMultipleActions();
 
       this.sendAsyncMessage("Content:Click", json);
     }

browser/actors/test/browser/browser.ini

@@ -1,3 +1,4 @@
+[browser_nested_link_clicks.js]
 [browser_untrusted_click_event.js]
 support-files =
   click.html

browser/actors/test/browser/browser_nested_link_clicks.js

@@ -0,0 +1,45 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Nested links should only open a single tab when ctrl-clicked.
+ */
+add_task(async function nested_link_click_opens_single_tab() {
+  await BrowserTestUtils.withNewTab(
+    "https://example.com/empty",
+    async browser => {
+      await SpecialPowers.spawn(browser, [], () => {
+        let doc = content.document;
+        let outerLink = doc.createElement("a");
+        outerLink.href = "https://mozilla.org/";
+        let link = doc.createElement("a");
+        link.href = "https://example.org/linked";
+        link.textContent = "Click me";
+        link.id = "mylink";
+        outerLink.append(link);
+        doc.body.append(outerLink);
+      });
+
+      let startingNumberOfTabs = gBrowser.tabs.length;
+      let newTabPromise = BrowserTestUtils.waitForNewTab(
+        gBrowser,
+        "https://example.org/linked",
+        true
+      );
+      await BrowserTestUtils.synthesizeMouseAtCenter(
+        "#mylink",
+        { accelKey: true },
+        browser
+      );
+      let tab = await newTabPromise;
+      is(
+        gBrowser.tabs.length,
+        startingNumberOfTabs + 1,
+        "Should only have opened 1 tab."
+      );
+      BrowserTestUtils.removeTab(tab);
+    }
+  );
+});