Yesterday I tried to open Firefox as usual from my task bar, but got the error that this program does not exist anymore (or something along those lines, I should have paid more attention). So I started Firefox from the start menu and immediately it looks like a brand new installation, with all bookmarks and passwords gone. I already tried the steps in this thread https://support.mozilla.org/en-US/questions/1235818 and the last one seems promising as there is another update folder from around the time I started yesterday, but I don't know how to restore that. I also located the profiles folder (it contains three) and identified my old profile, but the folder is completely empty.