whenever i clear firefox's history by "ctrl+shif+del", i get reverse caps-lock issue?

hi folks
everytime i clear ff's history via "ctrl+shift+del" combo before i close it, i get this awkward problem, reversed caps-lock, but only in firefox.
if i clear ff history with this combo and then try to type something in address bar before i close ff, it gets typed in caps-lock on mode, though it's not on.
and when i open a new tab and try to stop page from loading, the esc key won't work in this case. mouse keys change functions, etc.
also when i close ff main window, a second window is left open.
when i close ff completely, and relaunch ff, everything gets back to normal.
this strange caps-lock behavior and other issues only occurs in firefox.
any help would be appreciated.
thanks