1 files changed, 49 insertions, 0 deletions
diff --git a/browser/base/content/test/tabs/browser_blank_tab_label.js b/browser/base/content/test/tabs/browser_blank_tab_label.js
new file mode 100644
index 0000000000..9fe5f6b1b0
--- /dev/null
+++ b/browser/base/content/test/tabs/browser_blank_tab_label.js
@@ -0,0 +1,49 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Ensure that we don't use an entirely-blank (non-printable) document title
+ * as the tab label.
+ */
+add_task(async function test_ensure_printable_label() {
+  const TEST_DOC = `
+  <!DOCTYPE html>
+  <meta charset="utf-8">
+  <!-- Title is NO-BREAK SPACE, COMBINING ACUTE ACCENT, ARABIC LETTER MARK -->
+  <title>&nbsp;&%23x0301;&%23x061C;</title>
+  Is my title blank?`;
+
+  let newTab;
+  function tabLabelChecker() {
+    Assert.stringMatches(
+      newTab.label,
+      /\p{L}|\p{N}|\p{P}|\p{S}/u,
+      "Tab label should contain printable character."
+    );
+  }
+  let mutationObserver = new MutationObserver(tabLabelChecker);
+  registerCleanupFunction(() => mutationObserver.disconnect());
+
+  gBrowser.tabContainer.addEventListener(
+    "TabOpen",
+    event => {
+      newTab = event.target;
+      tabLabelChecker();
+      mutationObserver.observe(newTab, {
+        attributeFilter: ["label"],
+      });
+    },
+    { once: true }
+  );
+
+  await BrowserTestUtils.withNewTab("data:text/html," + TEST_DOC, async () => {
+    // Wait another longer-than-tick to ensure more mutation observer things have
+    // come in.
+    await new Promise(executeSoon);
+
+    // Check one last time for good measure, for the final label:
+    tabLabelChecker();
+  });
+});