Clear Private Data in Firefox under Ubuntu

I got Ubuntu 8.10 (Intrepid Ibex) and have a problem with clearing browsing history in Firefox 3.0.5. It always hangs and cleans nothing. So I deleted /home/user/.mozilla/firefox/26k93kik.default/places.sqlite 'cos it took up 900 MB(!) I also unchecked "Keep my history for at least" and "Remember what I entered in forms and the search bar".