1 files changed, 58 insertions, 0 deletions
diff --git a/docshell/test/browser/browser_onbeforeunload_nested_with_delay.js b/docshell/test/browser/browser_onbeforeunload_nested_with_delay.js
new file mode 100644
index 0000000000..409c73d0b7
--- /dev/null
+++ b/docshell/test/browser/browser_onbeforeunload_nested_with_delay.js
@@ -0,0 +1,58 @@
+"use strict";
+
+add_task(async function () {
+  const outer =
+    "http://mochi.test:8888/browser/docshell/test/browser/file_onbeforeunload_nested_outer.html";
+  await BrowserTestUtils.withNewTab(outer, async browser => {
+    let inner = browser.browsingContext.children[0];
+
+    // Install a beforeunload event handler that resolves a promise.
+    await SpecialPowers.spawn(inner, [], () => {
+      let { promise, resolve } = Promise.withResolvers();
+      content.addEventListener(
+        "beforeunload",
+        e => {
+          e.preventDefault();
+          resolve();
+        },
+        {
+          once: true,
+        }
+      );
+      content.beforeunloadPromise = promise;
+    });
+
+    // Get the promise for the beforeunload handler so we can wait for it.
+    let beforeunloadFired = SpecialPowers.spawn(
+      browser.browsingContext.children[0],
+      [],
+      () => {
+        return content.beforeunloadPromise;
+      }
+    );
+
+    // Register whether a load has started.
+    let loaded = BrowserTestUtils.browserLoaded(browser).then(() => "loaded");
+
+    // This is rather fragile, but we need to make sure we don't start a
+    // speculative load in the parent so let's give it the time to be done.
+    let timeout = new Promise(resolve =>
+      // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+      setTimeout(() => resolve("timeout"), 3000)
+    );
+
+    // Need to add some user interaction for beforeunload.
+    await BrowserTestUtils.synthesizeMouse("body", 0, 0, {}, inner, true);
+
+    // Try to start a speculative load in the parent.
+    BrowserTestUtils.startLoadingURIString(browser, "https://example.com/");
+
+    await beforeunloadFired;
+
+    is(
+      await Promise.race([loaded, timeout]),
+      "timeout",
+      "Timed out because the load was blocked by beforeunload."
+    );
+  });
+});