I still use Firefox as my main browser, but while it has improved a lot in recent times, I don't know why are some root problems not getting fixed - memory hogging, browser hangs, crashes (yes, I still get them on my workstation - I've even reported the callstacks to them). Mostly, the answer is, "It's your add-ons" - oh yes, but when it comes to talking about their strengths, this is one of the first things they talk about - "add-ons".
For example, every other browser fixed this 12 year old bug [0] one by one, but Firefox doesn't care much about it. In fact, not only that they don't have any solution to it whatsoever, when people's resentment about the bug increased, they chose to just shut down their voices on it.