Firefox is not an anti-virus and is not a replacement for one. That being said, there is no real need to pay for anti-virus either. Uninstall AVG and Avast, and install Microsoft Security Essentials. http://windows.microsoft.com/en-us/windows/security-essentials-download After installing it, run a full scan, update Windows, Update your plugins, http://www.mozilla.org/plugincheck/, and optionally, use the free tools at [[Troubleshoot Firefox issues caused by malware]] to double check you don't have anything malicious on your system. Keeping your software up to date is just as important to your PC's security as having an anti-virus.