I use Chrome. IE is actually banned from visiting external sites (not company sites) at my workplace!
I use Mozilla Firefox. A big portion of my job is coding, so I need to be able to pinpoint pieces of code on a webpage and Firefox is the only browser that includes a function to do this by default. Sure, any browser has the "view page source" function, but with Firefox, I can actually use the "inspect element" function to see the exact piece of code I'm looking for. Really handy tool!
Internet Explorer and Chrome. Chrome is actually used for only one of our applications because of the speed. Explorer for everything else as all the security precautions in place are setup for Explorer. Its a big bank...convincing them to use firefox will be a herculean task!!
IE is required on all of our machines as that is handled automatically in Microsoft's Group Policies. I also have Chrome loaded on there though.