hello, this sounds like the files in your profile folder that store the information about your extensions might have become corrupted. please go to firefox > help > troubleshooting information > profile - show folder... then windows explorer should open up your profile folder. in there look for the files named extensions.ini, extensions.sqlite, extensions.sqlite-journal (and in some cases also extensions.txt, extensions.rdf). delete or rename those files and quit firefox, they will be regenerated the next time you launch firefox.

also see Corrupt extension files

Thanks so much! Have a fun rest of your day!

I encountered a similar problem, and tried the solution suggested here. It did not work, and I was hassled with a lengthy series of tabs asking me to verify each add-on installation individually. (It even implied, incorrectly, that I needed to restart after each such approval.) Afterwards, my add-ons all still showed as being disabled in the sidebar, even though they were, in fact, working. Furthermore, the Enable and Disable buttons were not doing anything.

I decided the culprit might be All-in-One Sidebar. I installed the latest version, and the problem disappeared. In retrospect, I suspect that about:addons would have worked. It was just the sidebar access to add-ons that was fouled up.