I would be worried about the health of your computer. My work's T420 lenovo doesn't seem to lag THAT much, in fact, I hadn't noticed much of it until I got to read the comments here...

Scratch that, just after I wrote last paragraph I opened the site on Chrome (Instead of FF) and it lags heavily in there. I don't know if it might be because some FF plug ins block third party things like facebook connect and Google analytics...

I find it weird, the difference of fps between Chrome and FF with this site is HUGE in my computer.