Complaining about Internet Exploder has already been done to death, and the only people who still use it are old people who don't know what Firefox is and need their grandsons to install it anyway. That said, I'm a Mac user, so I get to complain about Safari instead.
It's rubbish. There. Got that out of the way. Version 4 had a remarkable tendency to crash every time I visited certain websites which is not a very good feature in a browser by and large. Version 4 was the version I had because I hadn't bothered to install system updates— it's a Mac so (a) there's no malware that needs to be patched against and (b) if there were, there would be no patch released because Apple dropped support in 1987.
Well I finally got around to installing the system updates and Safari 5.0.6 came with them. This version no longer crashes, but it's extremely slow and tends to go unresponsive for a minute or two whenever I try to load most web pages, and unlike the earlier version, it is not capable of playing netflix videos without dropping frames. So yeah, not a very good browser. But then, it makes sense that Safari would be crap— it's made by Apple.
Besides, I expect Mac users, as a group, contain a much higher percentage of old people who would need their granddaughters to install Firefox for them, given that Apple products have this bizarre reputation of "user-friendliness" (which ten minutes of using an iPhone would trivially disprove). Personally, I use Apple products because I'm allergic to paying money for things and I keep finding Macs for free in various bins.