Firefox Sync: End-to-End Encrypted Sync, Self-Hosting, and What Mozilla Can't See

Firefox Sync is Mozilla's encrypted sync service — it keeps your bookmarks, passwords, history, tabs, and extensions in sync across devices. Unlike Chrome Sync, Firefox Sync uses end-to-end encryption: Mozilla cannot read your data. This guide covers how it works, what syncs, and advanced usage.

How Firefox Sync Works

Firefox Sync uses end-to-end encryption:

1. You sign in with a Firefox Account (FxA) — your email + password
2. Your password is used to generate an encryption key (never sent to Mozilla)
3. Data is encrypted locally before upload
4. Mozilla stores only encrypted blobs — they cannot read your bookmarks, passwords, or history

The encryption keys are derived from your password using PBKDF2, then wrapped with a master key stored in your account. This is documented in Mozilla's open-source sync protocol.

What Firefox Sync Syncs

By default, Firefox Sync syncs:

• Bookmarks: full folder structure, all bookmarks
• Passwords (via Firefox Lockwise): saved usernames/passwords
• History: visited URLs and timestamps
• Tabs: open tabs on each device (accessible via "Send Tab" or the Synced Tabs panel)
• Extensions: which extensions are installed (not their data)
• Settings: some Firefox preferences
• Address Bar: search preferences

In Firefox Settings → Sync, you can selectively disable any category.

Setting Up Sync

1. Open Settings (hamburger menu → Settings)
2. Click "Sign in to Sync"
3. Create a Firefox Account or sign in
4. Choose what to sync
5. Confirm the device name (used to identify this device in synced tabs)

On a new device:

1. Sign into Firefox Account
2. Firefox automatically starts syncing
3. Your bookmarks, passwords, and history appear within minutes

Advanced: Sync Across Multiple Profiles

Each Firefox profile syncs independently:

Profile "Work": synced to [e-mail] Firefox Account
Profile "Personal": synced to [e-mail] Firefox Account

This way, work and personal data never mix. Both profiles can be open simultaneously with their own sync states.

Synced Tabs

Open tabs from other devices:

1. Firefox sidebar → Synced Tabs (or Tools → Synced Tabs)
2. See open tabs organized by device
3. Click any tab to open it on the current device

Send Tab: right-click any tab → Send Tab to Device → pick a device. The tab opens on the other device immediately (if Firefox is running there).

This replaces the "I'll email myself this link" workflow.

Firefox Sync and Passwords

Firefox Lockwise stores and syncs passwords end-to-end encrypted:

• Access at about:logins or via the key icon in the toolbar
• Generates strong random passwords
• Detects and warns about reused passwords
• Available on Firefox for Android via Firefox Preview/Fenix
• Can import from CSV (exported from Chrome, 1Password, etc.)

For teams or shared accounts: Firefox Sync is personal, not a team password manager. Use Bitwarden (FOSS) or 1Password for team password sharing.

Open Protocol: Self-Hosting Sync

Mozilla's sync server is open source. You can run your own:

# Using Docker
docker run -p 5000:5000 mozilla/syncserver

Then in about:config:

identity.sync.tokenserver.uri = http://your-server:5000/token/1.0/sync/1.5

This lets your organization control all sync data without any Mozilla involvement.

Firefox Accounts and Privacy

Firefox Account creation requires an email and password — Mozilla stores:

• Your email address (to identify your account)
• A stretched/salted hash of your password (cannot be reversed to your password)
• Encrypted sync data blobs (cannot be read by Mozilla)
• Timestamps of sync operations

Mozilla's Privacy Notice: Mozilla does NOT receive your browsing history, bookmarks, or passwords — only encrypted data.

Checking Sync Status

In Firefox:

• about:sync — shows sync status, last sync time, devices connected
• Settings → Sync → Manage account

Common sync issues:

• Sync stopped: check about:sync for error messages, usually re-signing resolves it
• Conflicting data: Firefox merges bookmarks from all devices; duplicates can appear
• Quota exceeded: Mozilla provides several GB of sync storage free; large history syncs can hit this

Tab Manager & Session Saver and Firefox Sync

Firefox Sync syncs which extensions are installed but NOT extension data. Your Tab Manager & Session Saver session data lives in the extension's storage (browser.storage.local), which is NOT synced via Firefox Sync.

For cross-device session access with Tab Manager:

• Export sessions to a file from one device
• Import on another device
• Or use browser.storage.sync (limited to 100KB) for small session snapshots

Using Firefox Accounts for Extension Development

Firefox Account enables:

• Signing in to addons.mozilla.org to manage your extensions
• Access to AMO developer dashboard
• Extension signing (required for self-distribution)

Your developer AMO account is your Firefox Account — same email/password.