I don't see any reason not to uninstall IE8 - I can't think of what would not work if you do. BUT - if I were you I'd just leave IE8 alone and install Firefox as a second browser. Most people do that. There is certainly nothing to be nervous about - you are not "changing" anything, just adding an additional browser which you can use instead of - or with - IE8 any time you like. Personally I have multiple browsers on most of my systems (IE8, Firefox, Opera, Safari).