Another problem with Firefox (especially on Windows) is the update mechanism. On Windows, it's an intrusive process that can't be scheduled, and on all platforms, there's the near-likely chance that an extension will be incompatible or that the UI will suddenly become just unfamiliar enough. Regular updates are generally a good idea, but Mozilla is pushing the experience to the limit of user patience.
Keeping up with and keeping ahead of the competition is okay, but Web browser choice is at last back, and there are some reasons why us Firefox users don't just switch. (Personally, I keep Opera, Chromium, Dillo, Lynx, and Links for regular use as well as Firefox.)