Given IE (and even Google Chrome) use Windows' protected mode to run in a sandbox, choosing Firefox over either of these (IE8, IE9, IE10, or Google Chrome) on the basis of security would be foolish. This isn't directed at you specifically (as you didn't mention security was the reason you choose FF over the others), but it is important to point out that IE8 and higher and Chrome (any version) on Windows Vista or higher would be more secure, browser-functionality-wise, than any version of FF on those platforms due to the security in place on the browser at low integrity when UAC is enabled.