Firefox add-ons were being disabled and failing to install on Firefox, now fixed
Anyone that uses Firefox as their default web browser might have noticed that most, if not all, of their add-ons stopped working over the weekend. This was an issue that impacted virtually every user that has add-ons installed.
As described in a post on Reddit's r/firefox community, the root cause of this widespread add-on issue is due to an expired security certificate. As the post summarizes, "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."
After this was discovered and widespread, Firefox's development team at Mozilla started developing a fix. Mozilla updated users on its work to rectify the issue via a post on its official add-ons blog. The issue was identified on Friday, May 3rd, with a temporary fix being released within 24 hours of the discovery. Unfortunately, that fix was far from ubiquitous, as it required users to download the fix from Firefox's “about:studies” Shield Studies (i.e. analytics) page. This wasn't universally seen by every Firefox user, with Mozilla recommending users "continue to wait."
On May 5th, a permanent solution was finally deployed. Version 66.0.4 on the stable release channel and version version 60.6.2 on the Extended Support Release channel rectified the issue completely. If you haven't updated Firefox yet, make sure to do so.
If this situation has you looking for alternatives to Firefox, you can find a selection of them here on AlternativeTo.