Firefox, Opera, Google Chrome all install on your PC alongside Internet Explorer so that one can have multiple browsers operating on a single PC.
Opera - www.opera.com/
Google Chrome - www.google.com/chrome
Firefox - UK version here - www.mozilla-europe.org/en/firefox/
You will have to select one as your default browser. You should be able to import your favorites from one browser to another. Forefox has lots of add-ons but be aware it can slow down loading.