Firefox add-on technology is modernizing
Add-ons such as Firefox extensions add extra features to Firefox. Anyone can create an add-on and make it available to Firefox users who want to personalize their online experience.
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. To address this (and other issues), we overhauled the underlying technology for building add-ons.
Outside of rare instances, add-ons created with the new standard, called WebExtensions, won’t break in new Firefox releases.
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. 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.
For more information about the new add-on technology in Firefox 57, see this Mozilla blog post.
If you are the developer of a legacy add-on, resources are available to help you migrate to the new standard.