Make appearance E2E platform deterministic

Signed-off-by: kenny lopez <klopez4212@gmail.com>

desktop/tests/e2e/buzz-theme-screenshots.spec.ts

@@ -745,7 +745,7 @@ test("prominent active tab is opt-in and switches selection surfaces", async ({
         PROMINENT_ACTIVE_TAB_STORAGE_KEY,
       ),
     )
-    .toBe("true");
+    .toBe("false");
 
   await toggle.click();
   await expect(toggle).toBeChecked();
@@ -1253,6 +1253,12 @@ test("accent picker reveals/hides when toggling Buzz", async ({ page }) => {
   // non-Buzz tile brings it back. Asserts the presence toggle (the motion
   // wrapper) works end to end.
   await seedTheme(page, "github-light");
+  await page.addInitScript(() => {
+    Object.defineProperty(navigator, "platform", {
+      configurable: true,
+      get: () => "MacIntel",
+    });
+  });
   await installMockBridge(page);
   await openAppearance(page, "light");
   await expect(page.getByTestId("accent-color-neutral")).toBeVisible();