I agree that memory issues are there with Firefox, still its relatively good browser than Chrome and IE when it comes to page load, stability and reliable surfing. Chrome often goes offline which requires a cookie clear and restart of the browser. It lacks add-ons, as effective as Firefox. IE has improved a lot with speed and security, still add-ons is a draw back. The GUI of IE is also not user friendly.
Apart from memory, it has everything under control. I am not concerned with that much, so Firefox is still my best choice!
PS: I am a Windows 7 user