Sync Tab Groups by Marmotz

Sync Tab Groups keeps your Firefox tab groups, and the tabs inside them, in sync across every desktop device signed in to your Mozilla account.

It relies on Firefox's built-in Sync storage: no server of ours is involved, and no data goes through any third party. The extension collects no data.

Features:
- Share a local tab group: its title, color, collapsed state and tabs (URL, title, order) become available on your other devices
- Live two-way sync: while a synced group is open on several devices, adding, removing or reordering tabs, renaming the group or changing its color on one device is applied on the others
- Custom tab titles: right-click a tab, then "Rename tab" (or "Reset title"). The custom title follows the tab in synced groups
- Open a synced group on a device where it is not open yet, and close it there without losing it
- Delete a synced group everywhere with one click
- Same-name conflict handling: when a local group already has the name of the synced group you open, choose to rename the local one, keep local tabs, keep cloud tabs, or merge both
- "Sync now" button to re-apply on this device the data Firefox Sync already received

Requirements:
- Firefox 140 or later (desktop only, Firefox for Android does not sync extension storage)
- A Mozilla account with Sync enabled and "Add-ons" ticked in Sync settings (about:preferences#sync)

Good to know:
- Propagation speed depends on Firefox Sync, which can take up to about ten minutes. Use Firefox's own "Sync Now" to speed it up
- Conflicts are resolved as last write wins
- Firefox limits synced storage to 8 KB per item: a group with a very large number of tabs may stop syncing. Splitting it in two works around it
- Only tabs inside tab groups are synced

Permissions: access to all websites is only used to display custom tab titles on the pages you renamed. Page content is never read or sent anywhere.

Source code and issues: https://github.com/marmotz/sync-tab-groups