All my extensions disabled themselves suddenly. Looking at the extensions page they all have a red box showing "X could not be verified for use in Firefox and has been disabled." Trying to install new extensions gives 'Installation aborted because the add-on appears to be corrupt.' Note that this didn't happen on startup, just while I was using the browser, which makes me think there's some periodic check thats failing?
Do you have anything at Tools -> Web Developer -> Browser Console?
If I try to install say dark reader: 1608054124271 addons.xpi-utils WARN Add-on addon is not correctly signed. 2 1608054124271 addons.xpi WARN Download of https://addons.mozilla.org/firefox/downloads/file/3684946/dark_reader-4.9.26-an+fx.xpi failed: signature verification failed I don't see anything about the existing disabled ones...
Looks like it's nss... *** This bug has been marked as a duplicate of bug 1908018 ***