Most of the comments here are about using or not using Firefox, depending on it's features as compared to primarily Chrome. However, for me, it is not about being better or having more features at all - it is because I like Firefox and want to support Mozilla and believe that Google should not control the web. It is somewhat similar to the free software vs. open source debate - one should use free software not becaus…
Firefox broke off backwards compatibility with massive amount of extensions - without them stock FF is quite shite and unusable. Not only that, some of the features of the old extensions are impossible to implement in the new extension engine.
Personally, I port my Chrome extension to a Firefox addons without much trouble, except for the stringent review process by a human developer which raised a lot my opinion of the firefox community.