I'm pretty sure you would never have given Mozilla any of your credit card or banking information. Does Mozilla sell anything? (T-shirts maybe.)

I suspect what you saw was a phishing scam, but the question is, did it come from a website you visited or from some software on your computer.

You may want to run some supplemental security scans. These two tools are highly regarded:

Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free (free version)

SUPERAntiSpyware : http://www.superantispyware.com/ (free version)

What you most likely have is what is called a Rogue Antivirus. http://en.wikipedia.org/wiki/Rogue_security_software

Download and Install MalwareBytes Anti-Malware, run a full Scan. http://www.malwarebytes.org/

Download and Run TDSSKiller http://support.kaspersky.com/faq/?qid=208283363

Download and Install Microsoft Security Essentials http://windows.microsoft.com/en-US/windows/products/security-essentials (not an official endorsement, but I personally recommend MSE as an awesome permanent anti-virus)

Double check for all Windows Updates.