Smart return to media tab after closing multiple tabs

[AdityaSK2401]

## Summary
When closing multiple tabs in sequence, Firefox currently switches focus to the most recently active or neighboring tab. While this is consistent, it is not always the most useful behavior in real-world multitasking scenarios.

## Problem
Users often keep one important tab open in the background, especially a tab playing media such as YouTube, music, livestreams, or podcasts. While working, they open and close several temporary tabs.

After closing those tabs, Firefox does not return to the media-playing tab. Instead, it switches to a previously active neighboring tab, which may not be relevant.

## Example
1. Open 8 tabs
2. Tab 2 is playing a YouTube video
3. Switch to tab 5
4. Close tabs 5, 6, 7, and 8
5. Firefox focuses tab 4
6. Expected: return to tab 2 (media-playing tab)

## Expected Behavior
Provide an optional feature or setting to improve tab focus behavior after closing multiple tabs:
- Prefer returning to the last media-playing tab
- Prefer pinned tabs
- Allow user-defined priority tab

If no such tab exists, fallback to current behavior.

## Why this is useful
- Reduces unnecessary tab switching
- Improves multitasking experience
- Better for users who keep one important media tab open
- Saves time in daily browsing workflows

## Suggested Approach
Firefox could track:
- Tabs with active media playback
- Pinned tabs
- A possible user-selected “priority tab”

Focus restoration could follow a priority order:
1. User-marked priority tab
2. Media-playing tab
3. Pinned tab
4. Default behavior

## Notes
This should be optional, so users who prefer the current behavior are not affected.

[Jon]

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