If you can't open Firefox then see:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter#Location_of_crash_reports
• http://kb.mozillazine.org/Mozilla_Crash_Reporter#Viewing_crash_reports

See also:

• http://kb.mozillazine.org/Firefox_crashes
• https://support.mozilla.org/kb/Firefox+crashes

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.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• Kasperky Free Security Scan: http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• http://support.kaspersky.com/viruses/solutions?qid=208280684

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Firefox 18.0.1 runs under safe mode, but once I reboot into "normal" mode, it begins crashing again.

If you have submitted crash reports then please post the IDs of one or more crash reports that have this format:

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

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, like you open a website.

See:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter
• https://support.mozilla.org/kb/Mozilla+Crash+Reporter

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.

• http://technet.microsoft.com/en-us/sysinternals/bb963902.aspx

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.

That makes sense. Thanks for the update.