Firefox, as it has become more popular, is now also targeted by malware vendors. Make sure you use the latest version and don't install extensions without doing the research.
You probably already know that as Internet Explorer is fully integrated into the Windows Operating System, keeping Windows up-to-date and patched is your first line of defence against malware. Despite using an alternate browser.
I am sorry to hear of the problem you had, that is a nasty experience no-one should have to go through. :(