TST Tab Favorites von hannu40k

Adds the following hotkeys and functions:

Ctrl + Right: Mark currently selected tab as a favorite tab (tab style is also changed).
Alt + Up: Jump to next favorite tab up from currently selected tab.
Alt + Down: Jump to next favorite tab down from currently selected tab.

Works well with one browser window.

Appears to occasionally have issues when multiple browser windows are used:
- Sometimes upon Firefox restart, the favorite tabs style is not immediately visible. Fix: The style should be restored when using the hotkeys to jump through the favorite tabs.
- If a tree of tabs is moved to another window, the visualization of favorites is carried over, but tab favorite status is not. Fix: Re-toggle affected tabs as favorite.