It seems like every thread talking about Firefox always has someone asking that question, so if you search back you should find plenty of reasons. Unfortunately, it’s been my observation that valid and polite criticisms always get downvoted. I don’t understand why. It’s not like downvotes are going to make the problems disappear.
Most of us would like Firefox to succeed, and it’s none of our faults that Mozilla is constantly neglecting it and going off on wild goose projects which get promptly abandoned.