Mozilla says that the issue is due to a certificate expiration, and that it's working to fix the issue. In a blog post, Mozilla says that it's identified the issue, and it's begun rolling out a fix for users. “The fix will be automatically applied in the background within the next few hours... Read on... Add-ons disabled or fail to install on Firefox (Redirected from Add-ons failing to install on Firefox) 9:31am PST, Please do not delete your add-ons as an attempt to fix. You will lose any data related to the add-on. Disabled add-ons will not lose any data. As of 8:13am PST, there is no fix available for Android. The team is working on it. From FF team FF Blog So don't uninstall , disable or delete your existing FF addons/extensions as FF has screwed it automatically from their ends. It will be fixed automatically. Make sure the mentioned options are set to enabled to get it fixed!! If you are still curious install the Hotfix manually from this link and all disabled add-ons etc are re-enabled once again.