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Mozilla released the Firefox add-on Disabled Add-on Fix for Firefox 47 - 56 yesterday, and Disabled Add-on Fix for Firefox 61 to 65, and Disabled Add-on Fix 57 to 60 on May 14, 2019, which resolve the add-on signing issue in older versions of the Firefox web browser when installed.

On May 3, 2019, Firefox users began to notice that something was not right. Installed add-ons were disabled by the web browser and there was no way to enable them again or install new extensions in the browser.

Firefox uses an add-on signing system to verify browser extensions. The system uses certificates to verify the legitimacy of add-ons, and one of the certificates used for that expired on that day. The expiration caused verification to fail for all add-ons.

Mozilla used various methods to get the situation under control. It used the browser's Shield system to distribute an emergency fix and released new Firefox versions that fixed it as well.

The fixes did not help users who ran older versions of the Firefox web browser or some third-party browsers based on Firefox code. Mozilla promised that it would release patches for older Firefox versions as well even though these are no longer supported by the company.

Disabled Add-on Fix for Firefox 47 - 56 is the result of that promise, or at least part of it as it fixes the add-on signing issue in Firefox 52 to 56. Disabled Add-on Fix for Firefox 61 - 65 addresses the issue in Firefox 61 to 65, and Disabled Add-on Fix for Firefox 57 - 60 in Firefox 57 to 60.

All that is required is to install the browser extension in Firefox to fix the issue. The extension installs a new certificate and enables extensions and themes again that were disabled.