Since upgrading to Firefox 18, I have been unable to start Firefox, even in Safe Mode. I have deleted my user profile and reinstalled Firefox twice. Clearing the user profile causes Firefox to offer to import from Internet Explorer, which I decline, after which is crashes. Subsequent starts result in crashes as well.
If you can't open Firefox then see:
Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.
Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.
You can also do a check for a rootkit infection with TDSSKiller.
If you have submitted crash reports then please post the IDs of one or more crash reports that have this format:
You can find the IDs of the submitted crash reports on the about:crashes page.
Which security software (firewall, anti-virus) do you have?
If it works in Windows Safe mode then you have a problem with other software, likely security software or a system driver, that is running on your computer.
Make sure that you have the latest updates of your security software.
You can use the Autoruns utility to see which software and services gets started.
Here are the crash reports I have submitted: bp-1c85bd40-cc52-44f0-82c6-759fc2130131 bp-333cce79-20cf-4669-9b7b-53ba22130131 bp-555e2095-0d9f-4f7e-ba74-7726a2130131 bp-ab12b1f6-af03-49fe-a73b-80e7a2130131
I have little reason to believe this computer is infected. I am running McAfee Enterprise 8.8i with the AntiSpyware plugin. I've also performed scans with Windows Defender and Malwarebytes Antimalware, which detected nothing that would interfere with the browser start (such as a malicious service or plugin).
This crash is caused by Websense Endpoint. Please contact them as you need to update your installation of Websense to fix this issue. They can assist you with that process.