Sounds like Safari is crashing. When an App crashes, the Mobile OS X tries to make it "elegant" but just shutting it down and sending you back to the Home screen. Some pages are just so (I would say poorly, but I'll be kind and say aggressively or busily) coded that they overwhelm Mobile Safari and crash it. Facebook profile pages, when filled to the brim with cr@p, do this a lot to me.
Hopefully the next version of Mobile Safari, with the SquirelFish Javascript engine will prove hardier. Or pages will get less cr@ppy.
You can also try going in to Settings > Safari and clearing your cache and cookies, to make sure all the gunk isn't bugging you up.