You def need both especially if you are developing stuff. I use ff for everything I can, some you do need IE though. Nothing makes more more mad than a site that forces you to use a certain browser or the site wont work. What I do hate is I have FF set as my browser but internally when using lets say messenger it will open up IE to check mail from messenger. If you set it as your preferred browser it should be honored by whatever OS you are using.
