One Tab Focus от Lamine

One Tab is a minimal focus tool that enforces a strict one-tab limit in Firefox.
When focus mode is on, any attempt to open a new tab is instantly blocked. No popups, no warnings — it just doesn't happen. Click the toolbar icon to toggle it on or off whenever you need.
While you're focused, a stopwatch tracks how long you've been in the zone, and a short message keeps you encouraged as the minutes add up — with new messages at 5, 15, 30, and 60 minute milestones.
That's it. No settings, no accounts, no tracking. Just you and one tab.
Features
• One-click enable / disable from the toolbar
• Instant tab blocking — no extra tabs survive
• Focus stopwatch that runs in the background
• Motivational messages at key milestones
• Zero data collected