This will be my very last attempt to help you. In order to possibly help you, I need information you have not provided. Please read all three requests carefully.
- Post your new dmesg.
- If X has failed and not restarted, post your /var/log/Xorg.0.log file. If X has failed but automatically restarts, post /var/log/Xorg.0.log.old instead.
- From an X terminal window, issue
$ script. A subshell will be opened. Issue $ firefox. If firefox fails and X continues to run, issue $ exit to close the typescript file, then issue $ col -b < typescript > my.console.output. If X fails while firefox is running, return to the directory where script(1) was running, then issue $ col -b < typescript > my.console.output. Post the contents of this file.