Firefox is not allowing users to install any of the listed add-ons due to a certificate issue, Mozilla confirmed in a forum post. The latest issue is also disabling existing add-ons and preventing users from enabling any installed add-ons on the browser. A large number of users have reported the existence of the issue through various online platforms, including Twitter and Reddit. However, it doesn't affect all Firefox users. The Firefox team is also providing updates through its Twitter account. While a general fix is yet to be released, Mozilla has started rolling out a fix using its Studies system to enable installing of add-ons through a workaround.
If you're among the users who have been affected by the newest issue, you would not be able to install any new add-ons or enable your existing add-ons from the Add-ons Manager on Firefox. The issue also affects the installing of themes on the Firefox browser.
The bug report related to the issue shows that it is affecting all the add-ons on Firefox due to an expired certificate. Separately, through an updated forum post on the Mozilla Discourse platform, the team has revealed that it has rolled out a fix for the general, beta, and nightly users of the Firefox browser on the desktop through its Studies system.
"In order to be able to provide this fix on short notice, we are using the Studies system. You can check if you have studies enabled by going to Firefox Preferences -> Privacy & Security -> Allow Firefox to install and run studies. You can disable studies again after your add-ons have been re-enabled. We are working on a general fix that doesn't need to rely on this and will keep you updated," the team wrote in the updated post.
Users presently need to use the given method to resolve the add-ons issue on Firefox. But nonetheless, it seems that the general fix would reach the browser shortly as well.