Firefox add-on technology is modernizing

Add-ons allow you to add extra features and functionality to Firefox, modify the Firefox user interface and change its appearance. There are several types of add-ons but extensions are the most common. Anyone can create an extension and make it available for download.

What's happening?

In the past, add-ons often stopped working each time a new version of Firefox was released, because developers had to update them every six weeks to keep them compatible. Since add-ons could also modify Firefox internal code directly, it was possible for bad actors to include malicious code in an innocent-looking add-on.

To address these issues, and as part of broader efforts to modernize Firefox as a whole, we’ve been transitioning to a new framework for developing Firefox extensions. Outside of rare instances, add-ons created with the new standard, called WebExtensions, won’t break in new Firefox releases. You can still personalize Firefox with add-ons the same way you do now, except they won’t break in new Firefox releases.

Note: Starting in Firefox 57, which will be released in November 2017, only add-ons built with this new technology will work in Firefox. These are indicated by the "Compatible with Firefox 57+" label on addons.mozilla.org (AMO). Add-ons built with the old technology are labeled "Legacy" in the Add-ons Manager (about:addons) tab.

If an add-on does not have the "Compatible with 57+" label or has the "Legacy" label, the developer may be in the process of transitioning to the new technology.

We are aware that certain add-ons will not be transitioning to the new standard; we will continue to assist developers to the fullest possible extent. As we get closer to November, we will suggest suitable replacements of add-ons not making the transition.

If you are a user of Firefox Nightly, please note that Firefox 57 reached the Nightly channel on August 2, 2017. Legacy add-ons will be disabled, but will be enabled again if the developer releases a compatible update.

In the meantime, you can check if an add-on is planned for migration (popular add-ons only), look for alternatives or reach out to the developer to inquire if they will migrate their add-on. You may find developer contact information on the right side of the add-on listing on AMO.

We recommend that you install add-ons with the "Compatible with Firefox 57+" label to ensure compatibility with Firefox beyond November 2017.

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