Update: Mozilla has issued a temporary fix for this issue. More information given at the end of the article.

Mozilla Firefox users are discovering that all of their addons were suddenly disabled. It turns out that this is being caused by an expired intermediary certificate used to sign Mozilla addons.

In numerous reports on Reddit, Twitter, and bug reports on bugzilla, users were stating that their Mozilla addons were suddenly disabled with a message stating that they "could be verified for use in Firefox".

Disabled Extensions

If they tried to reinstall the addons from the Firefox add-on site they are shown an error stating "Download failed. Please check your connection."

Error when installing an addon

From my tests, I was able to install some addons, but not others. This could be due to addons being signed by a different certificate that had not expired.

According to a bugzilla bug report, an intermediate signing certificate used to sign Mozilla addons expired on 5/4/19 at midnight UTC. As Mozilla addons have to be signed in order to be used in Firefox, once a computer reached that time the browser automatically disabled the addons.

Mozilla Bug Report

The last post in this bug report is from Kevin Brosnan, a senior quality assurance engineer at Mozilla, who stated that they are aware of the problem and are looking into it.

Mozilla looking into issue

Getting your addons working again

If addons are not that important to you, you can just wait for Mozilla to resolve the issue and your addons will start working again.

For those who do not want to wait and want to enable their installed extensions immediately, you have a few options:

Method 1: Turn your clock back a few days

The easiest method is to just turn your clock back a few days so that the certificate is not expired.

While this will work, it will also mean any site you go to with a certificate that expired today would work as well, your emails from a local mail client will have the wrong date, and some sites may show the wrong date.

Method 2: Install Firefox Nightly or Developer builds

Another option is to install the Developer or Nightly version of Firefox as these versions have the ability to disable the signature requirement for extensions.

To do this from the Developer or Nightly builds, you can go to about:config and search for xpinstall.signatures.required. Once at the setting, you should toggle the setting to false by double-clicking on it.

xpinstall.signatures.required setting

Once this setting is set to false, you should be able to use your disabled addons again.

Method 3: Enable addon debugging

A reader has offered the additional suggestion of enabling debug mode and installing the extensions locally from their XPI file.

"Just go to 'about:debugging' and check the box 'addon debugging', then load in the xpi file for the addons you need. Works for everyone and much less convoluted than the above mentioned workaround."

You can download addons directly from the Firefox Add-on site by right-clicking on the Add to Firefox button and select Save Link As... as shown below.

Download XPI File for Addon

Update 5/4/19 10:25 AM EST: Mozilla has stated that they are issuing a temporary fix through their Studies system. This system allows them to push out changes to Firefox without performing a full upgrade.

In order to use the Study system, you need to make sure it is enabled under Firefox Preferences -> Privacy & Security -> Allow Firefox to install and run studies as shown below.

In order to see if the addon fix has been installed by Firefox, you can go to about:studies and look for a study called "hotfix-update-xpi-signing-intermediate-bug-1548973" in the Active studies or Completed studies list. You may also see a study called "hotfix-reset-xpi-verification-timestamp-1548973" in the Active or Completed studies as well.

Hotfix shown in studies

If the hotfix is installed, you can disable the studies again if you no longer wish to receive them and your addons should be working again.