I understand that this is going to be a difficult adjustment, especially for long-time users. ALT+SHIFT+V is already in use (it invokes the View menu from the top menu bar). I also considered CTRL+SHIFT+V, but that is in use by Firefox as well (paste as plain text).
The Mozilla team is rolling out a fix for Firefox which should resolve the certificate issue affecting all add-ons. See their Twitter feed for details: https://twitter.com/mozamo/status/1124627930301255680