Subject: Xfinity Stream website loses its session on tab switch in Firefox — works fine in Edge and in a clean Firefox profile

Issue: On xfinity.com/stream (Xfinity Stream website), the Sign In button returns every time I switch away from the browser tab, even briefly. Returning to the tab shows the page intact but requiring a fresh "Sign In" click, which then re-authenticates silently — no username/password is requested. This proves my login cookies are intact; the Stream web app is discarding its own client-side session state whenever the page loses visibility.

Environment:
- Windows 11 (64-bit), Firefox 159.0 — latest release, fully up to date (also affected on Firefox 158.0.1)
- Microsoft Edge on the same PC, same network, same account: works perfectly — session survives tab switching with no sign-in prompts
- Reproduced in a completely clean, default Firefox profile (no extensions, no custom settings, fresh cookies) — same failure, so this is not caused by any user configuration on my machine
- Other sites (e.g., YouTube) hold their sessions fine in the same Firefox tab set; only Xfinity Stream loses state

Troubleshooting already performed in Firefox:
1. Updated to latest Firefox release (159.0)
2. Cleared all Xfinity cookies (69 stale tokens) and signed in fresh
3. Permanent cookie-allow exceptions set for xfinity.com and stream.xfinity.com
4. Enhanced Tracking Protection disabled for those domains
5. Firefox background tab unloading disabled (browser.tabs.unloadOnLowMemory = false)
6. Firefox background-timer throttling disabled (dom.min_background_timeout_value = 4, timer budgeting off)
7. Verified zero Firefox content-process crashes (Windows event log and Mozilla Crash Reports clean)
8. Full PC restart; behavior persists in Firefox only
9. Fresh-profile reproduction test with entirely default settings — same failure

Expected behavior: Stream session persists across tab switches in all major browsers.

Actual behavior: The Stream web app forfeits its in-page session in Firefox whenever the tab is backgrounded — including on entirely default settings — while working correctly in Edge under identical conditions on the same PC, network, and account. This is an Xfinity Stream web app compatibility defect with Firefox specifically, consistent with publicly reported Stream website issues previously acknowledged by Xfinity support.

Impact: Made effectively disruptive for watching television in one window while working in another; a click-through sign-in is required after each brief tab switch in Firefox only.