Firefox have had me. At first it came as the only true alternative to IE. I loved it very much. I installed some useful extension (Forecastfox for the weather, NoScript for security, Scribefire (formerly Performancing) for blogging, and DownThemAll for pr0n): they helped me to enjoy Firefox ever more.
But FF is a memory hog, and is slow, slower than IE? Sure is slower than Safari, today also in Windows flavor, which is pretty safe, pretty usable, and - damn - is definitely fast.
What I am about to miss: FF has a great way to handle rss feed as dropdown menu that is missing in Safari. Neither you can close tabs with the middle mouse button. Nobody's perfect.