This is a cheap, troll comment but it summarizes my views on Firefox. For a browser that started out in Linux, the lack of decent start times, page render times, and the same old tired Firefox 3.x interface in Firefox 4 is a huge slap in the face.
Now that Chrome will only load Flash on demand (and performance and stability of Linux Flash in Chrome is hugely improved as a result)... there is literally no reason for me to use Firefox 4.