macbookpro 2.4

I am having a malware problem with facebook. When i open facebook the top bar disappears so that i cannot open my messages or do any searches. also i cannot share. If i try to share it freezes my facebook and i have to shut it down.
I sent facebook messages as too my problems but no reply. I think I have a virus or malware problem....any insights?
Also my computer is running slow?
Should I run a malware/virus removal program on my mac? Which one?
Thanks

 

I haven't used it for a while but Sophos has a free program for OS X and is a reputable anti-virus company: http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx

Can you make another user account in System Preferences, log into that account and see if the problem occurs there also?
(You can delete that account later, it's just temporary)