Tab Drawers от Diar Sabri

Tab Drawers organizes your tabs into focused, switchable drawers — a modern,
maintained tab manager for people who live in their browser.

• Drawers, not clutter. Each tab belongs to one drawer. Switch drawers and
  only that drawer's tabs are shown; the rest are tucked away until you come
  back.
• New tabs join the drawer you're in, so your context stays clean.
• Save & reopen. Tuck a drawer's tabs away and reopen them later, right where
  you left off.
• Syncs across your devices through your own Firefox Account (end-to-end
  encrypted by Mozilla). No accounts to create, no servers, no tracking.
• Toolbar popup and sidebar, color-coded drawers, and keyboard shortcuts for
  next/previous drawer.

Open source (MPL-2.0). No analytics, no ads, and no data is sent to the
developer.