Start Firefox in -> Diagnose Firefox issues using Troubleshoot Mode to check if your add-ons/extensions are causing the problems.

• Also see this article -> Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Check and tell if its working normally while using Firefox in Diagnose Firefox issues using Troubleshoot Mode.

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

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

There is a possibility it s a malware problem

For cross referencing purposes

• Report for CrashID f735c3f7-9311-4d25-bc50-b3f2f2120522
• Crash Signature: RtlpWorkerCallout | RtlpExecuteWorkerRequest | RtlpApcCallout | RtlpExecuteWorkerRequest | BaseThreadStart
• related bug: Bug 599354 - crash under Windows XP in BaseThreadStart @ RtlpWorkerCallout (malware-related?)

This is a common crash signature, and there is a possibility it is related to malware.

• see also is my firefox problem a result of malware
• and a top contributors suggestions: /questions/914980#answer-302372