There's a lot to like about Firefox. Opera is still my primary browser. But there's reason for an assortment. I like opera for it's bigger feature set out of the box, tabs on the left, cloning tabs, etc. Chrome can't be beat for Google's sites like YouTube, gmail, etc. Firefox just plain works, for most sites, things like online banking, online shopping, etc, Firefox rarely lets me down always rendering the page correctly, cookie/session handling, handling referrals, downloads, etc. IE is unsurpassed for things like outlook web access, sharepoint, and the plethora of other Microsoft sites and Services. I don't have and interest in Apple material but I bet it's safe to assume all Apple stuff runs better on Safari.
While I like the Idea of using a single browser for everything, using that mentality is only going to limit your web experience. I like to think of browsers as shortcuts to different sites. Sure, windows media player can open an AVI file, but I'll associate AVIs with MPC-HC or Zoom player instead. Using this approach for websites is going to be better in the long run, because face it, as long as browser companies are creating web content there will always be preferential treatment for thier browsers.