Firefox enables user to install add-ons so as to increase the utility. Firefox ensures that the add-ons(which are basically third party code) are reviewed and signed (with a Mozilla certificate). These signed add-ons are available on addons.mozilla.org and also can be hosted on developers website. Now once you install the add-on in the Firefox, it looks for the certificate and allows only those add-ons which are signed by known Mozilla certificate. Rest every add-on is shown as corrupt.
Unfortunately the certificate is expired for now and hence all add-ons show as corrupt, Firefox add-ons team is working on it as of now and soon we will have a fix. Bugzilla entry
Follow this twitter thread for the fix progress (mozamo)[https://twitter.com/mozamo/status/1124484255159971840]
As a really quick workaround you can try ideas on this reddit thread but obviously these should be temporary!
Update
Top comments (3)
other browser vendors don't sign extensions, right?
Yes atleast to my knowledge Chrome and Opera does.
This fixed it for me discourse.mozilla.org/t/certificat...