With Firefox 57, scheduled for release in November 14, 2017, Mozilla will end support for legacy extensions, and only support newer WebExtensions. Here’s how to check if your extensions will stop working—and how to keep using them after November, if you need to.
Why XUL Extensions Are Going Away
All traditional extensions, including XUL extensions, are being discontinued. They were very powerful, but that was both a strength and a weakness. The sheer power of these extensions meant they could modify Firefox’s browser code, which could lead to instability and innocent-looking malware add-ons.
Instead, Mozilla has been working on WebExtensions, which are similar to Chrome and Edge’s add-ons. These are the future of Firefox extensions. Because these add-ons have to work in a more standard way and can’t mess with Firefox’s internal code, they should cause fewer problems. It should also be easier for developers to port add-ons from Chrome to Firefox.
Currently, Firefox supports both traditional (legacy) extensions and WebExtensions. With Firefox 57, the older extensions will stop working, and only newer WebExtensions will work. This change is already live in Firefox Nightly, the leading edge development version of Firefox. Developers have been pushed to upgrade their extensions, but not all have—which leads us to the problem.
How to See if Your Extensions Will Stop Working
if you use Firefox today, you can check to see which of your extensions will stop working in version 57. To check, click menu > Add-ons and select the “Extensions” category.
Older extensions that will stop working are labeled with a “Legacy” tag if you’re using Firefox 55 or newer. Modern WebExtensions that will continue working appear normally.
How to Search for New Extensions
If an extension has “Legacy” tag, you can check this list of popular extensions with information about their upgrade status. For example, in the screenshot above, LastPass is marked as Legacy extension that will stop working, but we can see that the developers plan to replace it with a WebExtension before Firefox 57’s release date.
For less popular extensions, you may need to perform a web search to see if the developer is planning an update. Developers have to port their extensions to WebExtensions, and not all developers will do so.
If an extension you depend on will stop working, you may need to search for a modern alternative that does something similar. You can search for only add-ons that are compatible with Firefox 57 or newer on the Mozilla Add-ons site.
Any add-on that has the “Compatible with Firefox 57+” tag is a WebExtension that will continue working. For example, the User Agent Switcher extension we have installed isn’t planned for an upgrade, so we probably want to install one of the more modern User Agent Switcher extensions.
This is a good time to evaluate whether you actually need all those extensions, though. Browser extensions can be dangerous, so it’s a good idea to only have them installed if they’re really useful to you and from a trustworthy source.
How to Keep Using Legacy Extensions
If you really require an old extension, there’s one way to keep using them safely. Switch to the Firefox Extended Support Release, also known as Firefox ESR. This is a slower-moving version of Firefox intended largely for businesses that don’t want major feature upgrades every six weeks.
The current Firefox ESR release is based on Firefox 52 and will be supported with security updates until June 26, 2018. As it’s based on Firefox 52, older extensions will continue to function without any problems
After June 26, 2018, you’ll have to upgrade to a newer versions of Firefox ESR that will no longer support legacy extensions if you want to continue receiving security updates. This isn’t a permanent solution, but it is a good way to keep using your current extensions for another seven months while you evaluate more modern alternatives.