Firefox needs to be careful...
...especially over plugins. Sooner or later they're going to break Flash (probably by mistake). As soon as they do that most people will defect immediately.
Also, they don't seem to realise that most people out there don't give a stuff for the technical advancements, etc. etc. All that most people want is a browser that just works OK in the same old way. People who use software get used to how it works and don't want it to change. Hasn't Mozilla seen the fuss over, for example, Microsoft's ribbon interface? Developers are practically the last people on earth who should be allowed to make UI design changes.