Create a new profile as a test to check if your current profile is causing the problems. See "Basic Troubleshooting: Make a new profile": * https://support.mozilla.com/kb/Basic+Troubleshooting#w_8-make-a-new-profile There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems. If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files. See: * http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox See: * http://kb.mozillazine.org/Firefox_crashes * https://support.mozilla.com/kb/Firefox+crashes * https://support.mozilla.com/en-US/kb/latest-firefox-issues

Thank you for your prompt reply. I tried to change profiles and it worked great. Also moved bookmarks, history etc. with no problem. I guess the problem was generated by an addon? But shouldn't firefox boot in safe mode? Anyway... Thanks again for the quick and to point solution.