Firefox bookmark issue

Hi guys, I have updated Firefox, and I was synchronizing my settings between Firefox installed on PC and Firefox installed on Linux mint (2 separate HD in the same PC case) when all of a sudden all bookmarks disappeared!! I have tried everything to recover them, profiles, restoring from menu, digging into various WIN/Linux directories, hidden files, JSON files, and so on, but nothing !! Looks like my bookmarks are vanished into a black hole. Is there any other method known to recover my bookmarks? (about 300 of them, divided in categories). I'm desperate!!