1 files changed, 70 insertions, 0 deletions
diff --git a/docshell/test/browser/browser_platform_emulation.js b/docshell/test/browser/browser_platform_emulation.js
new file mode 100644
index 0000000000..017b615e15
--- /dev/null
+++ b/docshell/test/browser/browser_platform_emulation.js
@@ -0,0 +1,70 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const URL = "data:text/html;charset=utf-8,<iframe id='test-iframe'></iframe>";
+
+async function contentTaskNoOverride() {
+  let docshell = docShell;
+  is(
+    docshell.browsingContext.customPlatform,
+    "",
+    "There should initially be no customPlatform"
+  );
+}
+
+async function contentTaskOverride() {
+  let docshell = docShell;
+  is(
+    docshell.browsingContext.customPlatform,
+    "foo",
+    "The platform should be changed to foo"
+  );
+
+  is(
+    content.navigator.platform,
+    "foo",
+    "The platform should be changed to foo"
+  );
+
+  let frameWin = content.document.querySelector("#test-iframe").contentWindow;
+  is(
+    frameWin.navigator.platform,
+    "foo",
+    "The platform should be passed on to frames."
+  );
+
+  let newFrame = content.document.createElement("iframe");
+  content.document.body.appendChild(newFrame);
+
+  let newFrameWin = newFrame.contentWindow;
+  is(
+    newFrameWin.navigator.platform,
+    "foo",
+    "Newly created frames should use the new platform"
+  );
+
+  newFrameWin.location.reload();
+  await ContentTaskUtils.waitForEvent(newFrame, "load");
+
+  is(
+    newFrameWin.navigator.platform,
+    "foo",
+    "New platform should persist across reloads"
+  );
+}
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: URL },
+    async function (browser) {
+      await SpecialPowers.spawn(browser, [], contentTaskNoOverride);
+
+      let browsingContext = BrowserTestUtils.getBrowsingContextFrom(browser);
+      browsingContext.customPlatform = "foo";
+
+      await SpecialPowers.spawn(browser, [], contentTaskOverride);
+    }
+  );
+});