Can I use two browsers at the same time?

Philippines
July 27, 2008 3:44pm CST
My computer is using Internet Explorer 6 as browser. But I want to use Firefox because of its feature of opening new tab unlike in IE where my screen is full of new windows! But I don;t want to quit IE because some of the sites that I joined in requires IE to be the browser when surfing. Can I use both browser at the same time? I already download Firefox 3 but have not installed it yet. If yes, what is the effect in my computer as a whole? Thanks!