Firefox Sync for Power Users: Cross-Device Tabs, Selective Sync, and Self-Hosting

Firefox Sync works well for personal use, but if you use Firefox professionally across multiple machines, here are some patterns worth knowing.

The Basics That Aren't Obvious

Firefox Sync is end-to-end encrypted. Mozilla servers store your synced data but can't read it — only devices with your account credentials can decrypt it. This is different from Chrome Sync, which Google can (and does) access.

What syncs:

• Bookmarks
• History (60 days by default)
• Open tabs (visible from other devices)
• Passwords (Firefox Password Manager)
• Extensions (installs them on other devices automatically)
• Settings (some, not all)
• Address bar shortcuts

What doesn't sync:

• Cookies and site logins (by design)
• about:config preferences
• userChrome.css
• Themes
• Pinned tabs (recently added in newer versions — check Settings → Sync)

Cross-Device Tab Access

The most useful feature most people miss: you can access tabs open on your other devices.

Firefox on desktop: Menu → Synced Tabs → see tabs from your phone, laptop, etc.

Firefox for Android: Menu → Synced Tabs → opens your desktop tabs on mobile.

Address bar shortcut: Type % (percent space) in the address bar to search only across synced tabs from other devices.

This is useful for: continuing work on your phone that you started on your desktop, sharing a link between devices without emailing yourself.

Partial Sync (Selective Syncing)

Settings → Sync → Check/uncheck what you sync.

If you only want passwords synced (not history), uncheck history. Useful for:

• Keeping work and personal browsing history separate when you use the same Firefox account on both work and personal machines
• Only syncing bookmarks and not exposing your browsing history to devices you share

Multiple Firefox Accounts for Separation

For complete separation of work and personal contexts (separate history, separate bookmarks, separate extensions):

1. Create a second Firefox account with a separate email
2. Use separate Firefox profiles (about:profiles) — each profile can be logged into a different Firefox account
3. Set Profile 1 = personal account, Profile 2 = work account

Profiles launch as separate Firefox instances. You can keep both open simultaneously with firefox -P profile-name --no-remote.

Sync Encryption Recovery

If you lose your devices, you can recover your synced data from the Firefox Account portal at accounts.firefox.com. Your sync recovery key is shown in Settings → Sync → Manage Account → Recovery Key.

Important: Store this recovery key somewhere secure. Without it, if you forget your account password AND lose your devices, your synced data (which is end-to-end encrypted) is permanently unrecoverable.

Using Sync for Tab Session Backup

Firefox Sync acts as a passive backup for your currently open tabs — if your computer crashes, the tabs from your session are visible from another device via Synced Tabs.

However, this isn't the same as named sessions. Synced Tabs shows you what's open right now, not saved sessions you can restore by name. For named sessions that persist across restarts and are restorable at will, Tab Manager & Session Saver handles this locally without any cloud.

Self-Hosting Sync (Firefox Accounts Server)

If you want complete control over your sync data, Mozilla provides the fxa-content-server and syncstorage-rs projects for self-hosting.

Simplified: you can run a Sync server at home and point Firefox at it instead of Mozilla's servers.

1. Deploy syncstorage-rs (Rust) or syncserver (Python legacy)
2. Configure a Firefox Account server (or use Mozilla's accounts but your own storage server)
3. In Firefox: set services.sync.tokenServerURI in about:config to your server

Full self-hosting with the accounts server is complex. Using Mozilla's accounts with your own storage server is more practical.

Sync Performance and Conflict Resolution

Sync can be slow on initial setup if you have large amounts of bookmarks or history. It uploads incrementally. If you've imported 10,000 bookmarks, give it a few minutes.

Conflict resolution: Last-write-wins for most sync types. If you delete a bookmark on one device while another device edits it, the deletion wins. Keep this in mind if you're doing bulk bookmark management — do it on one device at a time.

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Firefox Sync's end-to-end encryption is the key differentiator from Chrome. If privacy of your browsing history matters, Firefox Sync is significantly more private by design.