TabKeeper by Mateus Filpe

TabKeeper lets you take full control of your browser tabs and sessions. Save all your open windows and tabs as named collections and restore them any time. Supports Firefox tab groups with colors and titles.

Collections: save all open windows and tabs, restore in a new window or replace the current one, rename, duplicate, merge, or delete collections, drag and drop tabs and windows to reorganize, extract selected tabs to a new window.

History: automatically saves a snapshot every 5 minutes and on browser close, browse past snapshots grouped by date, save any snapshot as a permanent collection, keeps the last 50 entries.

Tab Selection: click to select tabs, Shift-click or Shift-Arrow to range-select across multiple windows, save, remove, extract, open, or copy URLs for selected tabs, full keyboard navigation with Arrow keys, Space, Enter, Escape, F2, and Delete.

Export and Import: export collections as JSON or plain text, import JSON or text files with support for multiple sessions.

Private Window Cookie Manager: export all private-window cookies to a JSON file, restore cookies and tabs back into an existing private window, clear cookies by domain or all at once.

Heavily inspired by the Session Buddy extension for Chrome. This is an independent Firefox implementation and is not affiliated with or endorsed by the Session Buddy project.