Tab Capper от CalStFrancis

Tab Cap enforces a hard limit on the number of tabs you can have open at once. When
you try to open a tab past your limit, it's immediately closed and a notification
reminds you to close one first — no silent behaviour, no guessing why a tab didn't
open.

Features:
- Set any limit from 1 to 200 tabs
- Pinned tabs are excluded from the count — they're tools, not clutter
- Per-window mode: enforce the limit on each window independently instead of
globally
- Live toolbar badge shows your current tab count at all times, turning red when
you hit the limit
- Tracks how many tabs you've blocked today
- Adapts automatically to your Firefox theme — light, dark, or any custom theme
- Keyboard shortcut: Alt+Shift+T (rebindable in Add-ons Manager)

Tab Cap is useful if you find yourself with dozens of tabs open and want a firm
boundary to work within. The limit is yours to set and change at any time from the
toolbar popup.