As said in the question, basically whenever I restart my firefox, it shows the first run screen, even though there was no update. I can recover my tabs and everything. Settings, bookmarks, history etc. stay the same. At the same time, all my addons (besides the GMX MailCheck one which prompts me to log in again and is doing its "first run" thing as well) are disabled. For some reason, even Pocket (which I actually use and is pretty hard to disable from what I gathered) is gone from all menus. I once managed to enable it again after accidentally finding an addons option in CC cleaner, but the next restart removed it again. Reinstalling firefox solved the problem for a while, but by now it's happening again. The Addons are not deinstalled or anything, a simple reactivation solves most issues, but this is really annoying given that GMX MailCheck tries to force their own "new tab" and "start" websites, as well as their own search bar etc. down my throat every single time... My problem is that I need it, given that my email accounts run over GMX. It's just weird that it remains the only addon that stays enabled. Besides GMX I basically only use adblock plus and Xkit (which is a tumblr improvement addon), the other addons remain deactivated unless I need them.