see this for help:

Recover lost or missing Bookmarks

Been there, done that. All the profile files I can find are blank, along with all my browsing history before the Office update this morning.

And resetting to defaults doesn't help either.

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences

Have you checked the trash / recycle bin?

Been there, done that, again.

After this, if I don't get a quick solution I'm going to ditch Firefox and rebuild everything on another browser.

The files may have been overwritten. Some special software might find it, but I don't know how.