Frequently asked questions - Firefox add-on technology is modernizing

This article is no longer maintained, so its content might be out of date.

What is a legacy extension?

Extensions built using frameworks that are not compatible with Firefox 57 and beyond (such as SDK or XUL) are considered “legacy” extensions.

How can I tell if I have any legacy extensions installed?

To see if you have incompatible extensions installed, go to the Add-ons Manager. Click the menu button Fx89menuButton and choose Add-ons and themes or enter about:addons in a new tab. If you have a legacy extension, it will display as disabled and the toggle to enable it won't display.

Can you recommend replacements for my legacy extensions?

We recommend that you search for compatible extensions on (AMO) or look through the featured extensions collection.

Alternatively, you may use the extension finder utility to look up the extension you would like to replace and discover recommended replacements.

There aren’t any recommended replacements for one of my legacy extensions. What now?

If you don’t find a suitable replacement, please head over to our forum to ask the community for suggestions.

When did Firefox ESR stop supporting legacy extensions?

Firefox Extended Support Release (ESR) version 52 was the last version that supported legacy extensions. Support for ESR 52 ended on September 5, 2018.

In October 2018, all legacy add-ons were disabled on (AMO). Users will no longer be able to find legacy add-ons on AMO.

If you decide to run unsupported releases to use legacy add-ons, this will make you vulnerable to security weaknesses, and we strongly do not recommend that they be used.

What happened to my complete theme?

Complete themes do not work with Firefox 57+ and are disabled. If you use a dark complete theme, the Dark Theme option in the Add-on Manager might be a good option for you. Go to the Themes tab in about:addons and give it a try. We are making improvements to themes in the coming months, so look for themes with additional functionality beyond an image overlay in future releases.

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