If I use Mozilla Firefox will my computer still get viruses, and if so, how can I check my computer for viruses and malware?

I use Mozilla Firefox. I recently opened an email on AOL that was appears to be from someone’s hacked email account. This person’s email account has sent me several things which appear to be hacked, and the last one that I accidentally opened said it had viruses in it. I closed the computer down (after trying to “x” out of the sites) but I just want to check that there were or are no viruses that made their way through.

How can I check my computer (myself) for viruses or malware? Or should having Mozilla Firefox be effective enough?