How to Fix Incompatible Firefox Extensions (2026 Guide)

Updated Firefox and now your favourite add-on has stopped working? Incompatible Firefox extensions have annoyed users since the early days. In 2006 the fix was to edit an extension’s install.rdf file and raise its “maxVersion” number. That trick no longer works, because Firefox switched to a new extension system in 2017. Here is how to fix incompatible Firefox extensions in 2026.

Quick answer: Open the Add-ons Manager (Ctrl+Shift+A), click the gear icon and choose “Check for Updates”. If the extension is still disabled, remove and reinstall it from addons.mozilla.org, test in Troubleshoot Mode, or refresh Firefox. If the add-on is a legacy extension from before Firefox 57, it can never run again, so install a modern alternative.

Why Firefox extensions become incompatible

• Legacy add-ons: Firefox 57 (Quantum, 2017) dropped old XUL and bootstrapped extensions. Only WebExtensions work now.
• Unsigned extensions: release versions of Firefox only run add-ons signed by Mozilla. An add-on installed from a random site may be disabled.
• Abandoned add-ons: if the developer stops updating, an extension can break when Firefox changes an API.
• Corrupt profile data: a damaged add-on database in your profile can show working extensions as broken.

How to fix incompatible Firefox extensions

1. Update all add-ons

Type about:addons in the address bar, click the gear icon and select Check for Updates. Most problems disappear once the developer’s update installs.

2. Reinstall from the official add-ons site

Remove the extension, then install it again from addons.mozilla.org. This fixes signing errors and partial downloads.

3. Test in Troubleshoot Mode

Click the menu > Help > Troubleshoot Mode (it used to be called Safe Mode). Firefox starts with all add-ons disabled. If the problem goes away, turn extensions back on one by one to find the one causing trouble.

4. Refresh Firefox

Go to about:support and click Refresh Firefox. This resets settings and removes add-ons but keeps bookmarks, passwords and history. Reinstall only the extensions you need.

5. Check the developer’s page or support

On the add-on’s page, check the “Last updated” date and reviews. If other users report the same problem after a Firefox update, the developer is probably working on a fix.

6. Find a modern alternative

If the add-on has not been updated for years, search addons.mozilla.org for a replacement with recent updates and good ratings. For example, see our picks of Firefox extensions to manage tabs.

What about forcing compatibility?

Old tricks such as Nightly Tester Tools, editing install.rdf or changing extensions.checkCompatibility in about:config do not work with modern Firefox. Turning off signature checks (xpinstall.signatures.required) only works in Firefox Developer Edition, Nightly, ESR and unbranded builds, and it is risky because unsigned add-ons are not reviewed by Mozilla. For most people, a supported alternative is the safer choice.

Good news for ad blocker users

Chrome has moved to the stricter Manifest V3 extension rules, which limit some ad blockers. Firefox supports Manifest V3 but has kept support for the older blocking features, so full versions of extensions like uBlock Origin still work in Firefox.

FAQ

Why does Firefox say my extension “could not be verified”?

The add-on is not signed by Mozilla. Reinstall it from addons.mozilla.org, or remove it if it is not listed there.

Can I go back to an older Firefox version?

You can, but older versions miss security fixes. Fixing or replacing the extension is safer.

Do Chrome extensions work in Firefox?

Not directly, but many developers publish Firefox versions of their Chrome extensions on addons.mozilla.org.

Which Firefox add-on can you not live without? Tell us in the comments.