Hello Joko.

Can you be a bit more specific about what you did and how it didn't work?

See http://kb.mozillazine.org/Firefox_crashes and Troubleshoot Firefox crashes (closing or quitting unexpectedly)

If you have submitted Breakpad crash reports then it might help if you post the IDs of one or more Breakpad crash reports.
You can find the IDs of the submitted crash reports on the about:crashes page.
You can open the about:crashes page via the location bar, just like you open a website.

See: http://kb.mozillazine.org/Breakpad (Mozilla Crash Reporter) and Mozilla Crash Reporter: Breakpad

I too have this problem. In my case, my PC is in good shape with regular maintenance, so no spyware or virus probs. I decided to install SP3 on my Windows XP, and immediately my Firefox ceased to fire up. Also Windows Update fails to work. Internet Explorer 6 works ok, but I really want Firefox working again. First time this happened, I removed the SP3 installation, by restoring an earlier backup. However later on I discovered that another program that I run, needs SP3 installed. So I reinstalled SP3 once more. Once more Firefox fails to run. I click on the icon to fire up Firefox... but nothing happens. I have reinstalled Firefox... again, nothing. I've also run 'dial-a-fix' with no improvement. Incidentally, I also have trouble with I/Explorer 8 not installing.

Same problem as Nirananda....

My pc run XP SP3 in korean..... I've been using firefox 3.6 with no issues. I upgraded to version 4 and the application didn't run. Even that in the task manager is runing a process called firefox.exe.

The Safe Mode didn't appear on the start menu.

I reinstaled an unistaled several times but can't fix the problem. I JUST MOVED TO GOOGLE CROME.....

Any advice???