I know I've dropped Firefox across the board. When Firefox 4 comes out, I'll give it a shot. It's slower to open, slower to load pages, slower to close, requires restarting on plugins and themes, flash crashes the whole browser, etc.
I don't know why anyone's using Firefox 3.x outside of some yet-unported extensions.
I don't know why anyone's using Firefox 3.x outside of some yet-unported extensions.