I've installed "myFox", a port of FireFox to the iPhone. It's very similar to Safari and it's been pretty much as capable or incapable as Safari has at displaying pages. It also does not support flash. You have to be jailbroken to use it.
However showguy is completely correct about reminding you that you're using a phone's web browser. You can say it "should" be just as able to render web sites like a computer all you want, but that doesn't mean it can. The iPhone has the best browser I've seen on any phone, but it's still just a phone with a phone's cpu and limitations.