Add-on Sync Coming to Firefox

We strive to make your online experience better and we have a new feature in the latest Firebox Beta we think you’ll love: add-on sync.

Add-on sync does what its name implies: it synchronizes add-ons between profiles connected with Firefox Sync. Specifically, it will install, uninstall, enable, and disable add-ons across your devices as you do.

If you are a new Sync user, add-on sync will be enabled by default. However, since Mozilla cares about your privacy and we don’t want to do anything without your explicit permission, existing Sync users will need to manually opt in to the feature. This can be done through the Sync tab in Firefox’s Preferences window. Explicit instructions are available at

Once you have add-on sync enabled, you don’t need to do anything special to get your add-ons to sync. As you use your browser, Sync will run in the background. As it does, the current state of your add-ons will be collected and sent to the sync server. As you use your other devices, Sync will apply changes to your local Firefox. Add-on sync runs in the background and you won’t see any pop-ups indicating it is running. And, since some add-ons require a restart for changes to be made, you may not see your new add-ons until you restart your browser. Our studies show that over 99% of Firefox users restart their browser at least daily, so you shouldn’t have to wait too long. If you are curious, you can open the Add-on Manager (about:addons) and see what changes will occur on the next restart.

There are a number of challenges involved with synchronizing add-ons. Because of this, the scope of the initial add-on sync feature has intentionally been limited. For this initial release, an add-on will be synchronized only if all of the following criteria are met:

  • It is an extension or theme
  • It is installed from
  • It is publicly listed on the add-ons site
  • It is installed into the current profile by the user

For now, add-ons are only synchronized between identical application types – changes to a desktop browser will only affect other desktop browsers and changes to a mobile browser will only affect other mobile browsers. Greater functionality between desktop and mobile will come in the future.

Security and privacy are important concerns when designing add-on sync. As with all your Firefox Sync data, add-on data is encrypted in your browser before being transmitted to the Sync server. So, people in the cloud can’t tell what add-ons you have installed, even if they wanted to know.

Add-on sync is a feature in progress and are working on further updates to include in later Firefox releases. You can learn more about add-on sync including background on some key design decisions at If you would like to get involved, instructions for reaching us can be found at

We hope add-on sync makes managing your online experience with Firefox a little easier. Happy syncing!

6 responses

  1. Anonymous wrote on :

    Since Sync uses client-side encryption, why do you say that “since Mozilla cares about your privacy and we don’t want to do anything without your explicit permission, existing Sync users will need to manually opt in to the feature.”?

    1. mconnor wrote on :

      Add-ons running in your browser can access your private data, and not every user syncs all other data. As a result, installing add-ons across all installs by default could create a privacy concern, without warning. We’ve erred on the side of caution here, based on our principles.

  2. maki wrote on :

    Nice for people using many extensions. The thing I’m waiting for is Search Engine Sync, which has unfortunately TBD date on the wiki:

    I’m not sure why, as setting up search engines is time consuming, partly because Firefox does not have a tool to create “search engines” by eg. right clicking a search field (like Opera does).

    There’s Bug 335781 which suggests to move search engines to the add-ons page, will this speed up search engine sync deployment?

  3. TJ wrote on :

    This is the best news yet! I was hoping something like this would come to Firefox. Now it can definitively compete with Chrome. Add-on syncing is really the only thing I “love” about Chrome­—and now I don’t have to use Chrome anymore.

  4. Kevin Granade wrote on :

    I think this is one sync feature that I’ll want to have a bit more configurability than the rest, there are a core group of Add-ons I want installed on all of my Firefox instances, but another subset that I only want on some of them, e.g. I keep the number of add-ons running on my EEE PC to a minimum.

    Glad to hear about the feature in general though, been looking forward to it.

  5. Felix Nagel wrote on :

    Sounds great, Im looking forward to test this!

    And I agree with maki: Now only search engine sync is left on the todo list 😉