New 2011 iMac sluggish

Long story short:

Just had a power outage.
Mac cut off.
Turned Mac back on.
Started Firefox.
EXTREMELY sluggish performance.
Safari is much better but something still doesn't feel right.
Tried reinstalling Firefox, no luck. Firefox freezes and won't close unless it is forced.

Any ideas guys? Why would Firefox all of a sudden turn rotten just because of a little power outage?

Mind you, I have no surge protection or anything at the moment but I have just ordered an APC 1000w UPS backup unit.

When you have unexplained problems, first thing to try is to repair the hard drive. To do a complete repair, you need to be booted from another drive, like from the DVD/CD drive. Follow this guide down at the section titled "Try Disk Utility."
Resolve startup issues and perform disk maintenance with Disk Utility and fsck

Well, since you just bought it, you could take advantage of the warranty still on the machine and return it for a free repair. Better to have them check it for any hardware problems before the warranty runs out and it just dies on you, it makes for a expensive paper weight.

^second that

I bought a new iMac 27"with i5 a couple of weeks back and it runs like Lightning on everything.

Why not simply uninstall Firefox - and download a new program ?

Hope your power cut didn't lead to a surge when it came back though.