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Firefox Disabling add-ons or marking them as legacy – here’s how to fix it

Have your FireFox add-ons been disabled with a message like “could not be verified for use in Firefox and has been disabled”? Do all your add-ons appear under “unsupported” as Legacy Extensions?

Well, this is what happened, and I’ve got two workarounds until Mozilla fixes the problem:

What’s going on?

A few hours ago a security certificate that Mozilla used to sign Firefox add-ons expired. What this means is that every add-on signed by that certificate, which seems to be nearly all of them, will now be automatically disabled by Firefox as security measure.

In simpler terms, Firefox doesn’t trust any add-ons right now.

Here’s the official acknowledgement from Mozilla on their Discourse:

Certificate issue causing add-ons to be disabled or fail to install

At about 6:10 PST we received a report that a certificate issue for Firefox is causing add-ons to stop working and add-on installs to fail.

Our team is actively working on a fix. We will update as soon as we have more information.

Update:

11:12 p.m. PST: The team is currently testing a fix for this issue. In the meantime, signing of new extensions is disabled until the fix is in place.

How do I fix this?

You can either 1: Temporarily load extensions, or, in some editions of Firefox, 2: Disable signature enforcement, telling your browser to trust all extensions.

These editions are Firefox Developer Edition, Firefox Nightly, Extended Support Release, and the Unbranded builds. There are some reports that you can disable signature enforcement on Linux or OSX regardless of Firefox ediiton. You can migrate to one of these editions using Firefox Sync or by telling it to use your original profile.

If you aren’t sure which edition of Firefox you’re on, it’s probably Release, but you can see for yourself by heading to ☰ > Help > About Firefox.

1: Temporarily loading extensions

Extensions installed via Firefox’s debugging tools are installed “temporarily”, meaning they will be automatically disabled again on browser restart.

All of your extensions currently reside in the “extensions” folder inside your profile folder. Go to ☰ > Help > Troubleshooting Information, then copy or make note of your “Profile folder” in the table.

Next got to about:debugging and click Load Temporary Add-on…. Navigate the file dialog to your profile, then to the “extensions” folder inside. You should see a list of .xpi files – these are your add-ons. Load one, then repeat for all of them.

Note: This method can also be used to install add-ons from addons.mozilla.org. Simply navigate to the extension page (such as uBlock Origin) and right click on the “Add to Firefox” button, then select “Save Link As…” and load it as described above.

2: Disabling signature enforcement

In a supported build, enter about:config into the location bar and push enter. Heed the warning and proceed to search for xpinstall.signatures.required and set it to false.

This tells the browser to no longer care if installed extensions are what they say they are. This is a light security risk, and you should re-enable this once the certificate issue is solved.

All your add-ons should automatically re-enable.

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