How to completely remove Xmarks from Firefox?

[box o rocks]

I already did the "remove" in FF Extensions. But I'm still getting the xmarks popup telling me there was an error syncing. What I've tried:
1) Shut down/restart FF
2) Reboot the PC
3) Run CCleaner (Clean and Registry options)
4) Swore at the screen

Is there somewhere xmarks is hiding in the Win 10 registry maybe? Should I search for and remove every instance that "xmarks" or "last Pass" shows up?

 

[Alabalcho]

Have you tried opening Firefox with another user profile?
Open "Command prompt", and execute

C:\Users\Me>"c:\Program Files\Mozilla Firefox\firefox.exe" -p

Replace "Program files" with "Program Files (x86)" if you have 64-bit system with 32-bit FF.

 

[box o rocks]

Well... doing that was sure a mistake!