Based on the "More system details" you posted, I found the crash report at http://crash-stats.mozilla.com/report/index/17dc3303-addc-42a0-af8e-a63472110924 which shows:

Firefox 6.0 Crash Report [@ nsStandardURL::SchemeIs(char const*, int*) ]
ID: 17dc3303-addc-42a0-af8e-a63472110924
Signature: nsStandardURL::SchemeIs(char const*, int*)

... and links to two bug reports that indicate that the crash is caused by malware.

• Bug 680418 VERIFIED DUPLICATE Cannot start Firefox after v6 update. Crashes and won't start, even in Safe Mode.
• Bug 670542 VERIFIED FIXED Crash in nsStandardURL::SchemeIs or nsSimpleURI::SchemeIs mainly close to startup, mainly with a random .cpl or .dll filename in stack (malware-related)

See Troubleshoot Firefox issues caused by malware under "How do I get rid of malware?" for recommended ways to remove the malicious software that is causing your crashes.

Do a malware check with some malware scanning programs.
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/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

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