Firefox closes on start-up and re-opens empty, master password dialog doesn't appear.

My firefox has been acting weird all of a sudden. Usually when I open firefox it loads all my tabs of the previous session and prompts me to enter my master password. But now when I start firefox, it opens for a brief moment and then instantly closes again. When I open firefox again all I get is a new empty window without any tabs, the password prompt also doesn't appear. So I have to manually open my last closed window to get the old window with all the tabs back (so I guess the window that closes instantly was the proper one) but the master password prompt won't show up. I can't access all my saved passwords in the password manager since I'm expected to sign in but when I click on "sign in" nothing happens - I guess the master password dialog just doesn't show up blocking me out of it. The only solution I have found so far is to go to about:support and clear start-up cache data. When it reopens afterwards I get the working window back, with my saved tabs and the master password dialog shows up - everything works. But it only works for this session, when I reboot the computer I have to do the whole issue again. Opening it in safe-mode also works but I need my addons and since it starts after clearing startup cache I don't think the addons are to blame. It just happened all of a sudden, I didn't install any updates or new version prior to the error.

Can anyone please help me? :(