I've used Firefox exclusively for the last 5 years or so and haven't missed IE in the slightest. Problem wit IE is that it's tied into Windows so it'll never be able to just do 'the internet', it's weighed down with a load of crap before you've started.
I'm a big fan of open source software, I use loads of it where I can, Seamonkey instead of iTunes, Gimp instead of PS, OpenOffice instead of MS Office. The latter is worth a look as well as again, I have used it exclusively for the last few years and have always done all my invoicing and quoting etc... with it and have some pretty good spreadsheets going on, can't see why anyone would use Office.