Group Tabs By Domain Easy от plucafs

Tab Organizer adds an "Organize tabs by domain" entry to Firefox's right-click tab context menu (also available via Ctrl+Alt+O).
Groups all ungrouped tabs in the current window by their domain name:
- Tabs sharing the same domain are placed into a named, collapsed group with a deterministic color
- Tabs with a unique domain are moved to a generic "Ungrouped tabs" group (grey)
- Pinned tabs, already-grouped tabs, and about: / file: pages are skipped
- The www. prefix is stripped before grouping
- If more than 15 tabs would be affected, a confirmation popup is shown before proceeding