Please, just fast and user-friendly
I used to loath IE, but it's now pretty high on my list of favourite browsers considering how irritating Firefox has become in its goals to produce endless more good ideas that no one thought through.
IE was basic, too basic as it didn't even adhere to some pretty simple and widespread standards. That's all gone now and it's a delight to use. And that's coming from a guy who uses Safari on his Mac at home.
Firefox had so much promise, but like all spoilt children it has grown up to be arrogant and useless; and impossible to live with. I can't browse without endless security popups, which are due to very good reasons but can't be turned off. It's slow to start, fails to load the tabs I set in the options, fails to respond smoothly to almost all interactions and.... I have a fast machine with plenty of memory. And that's Windows. On the Mac it's even worse.
No support for standard controls in either OS due to skinning and plugins. They need to go back to scratchboard, remove all the stupid pretty features that bog it down and stick to what they first promised to deliver: a good, fast, reliable and secure browser. Not secure as in a chastity belt, secure as in secure software that keeps me aware of what's going on.