I upgraded to Mozilla 1.2 this morning, on Mac OS X. It hung on startup, trying to create the first window.
I duplicated ~/Library/Mozilla/ in case I broke something, then deleted the Application Registry file inside that folder, and then started Mozilla. It asked me to create a new profile; I obliged. New profile, I want my old prefs back. I quit Mozilla, copied the contents of my old profile into the new one, and then started Mozilla again. Everything back to normal.
Although, I cannot tab in between form elements anymore. I used to be able to select form elements with tab. What gives?