Whether you remove IE is completely up to you. Firefox is my default browser, but I still keep IE though I don't use it.
My only tip for Firefox is you should get the McAfee SiteAdvisor tool (google it).
It's a tool for Firefox that rates each page you visit with either a checkmark, an "X", or a "?" and it basically tells you if that page is dangerous.
It works with google searches too, where it has one of its three symbols beside each of your results, basically telling you which pages you should and should not go to.