Should I revert firefox to a previous version so an (important) add-on can work?

All said_ I used TMT (too many tabs) daily and have stored loads of pages I intend to flip through when I have the opportunity. This week_ I assume _ the browser updated automatically (on Ubuntu using Unity) to version 21.0. This add-on is not functional on this version, so all my tabs are somewhere in the ghost realm.
I’ve scanned threads on the topic, but I can’t quite find a time saving direct answer that offer an actual solution to the problem.
Thus, here I am consulting with me mates on fluther…