The Add-ons team is working on a fix for this. It looks like a certificate used to sign many popular extensions expired. (The verification process checks that certificate.)

I don't know how soon re-signed versions of those extensions will become available, or whether another workaround will be discovered. We are all hoping to learn more soon.

ok thank you hopefully this will be fixed soon, also is this the reason i cant download any new ones right now?

I must be having the same problem. All of my extensions were just simultaneously disabled. When I try to re-add them, or add any new extension, I get the message, "Download failed. Please check your connection." (My connection is fine.)