The nicest thing I can say about FF is that it opened the floodgates, before Firefox/Phoenix/Mozilla Suite you had crappy IE, broken NS, and adware Opera.
Today there is Comodo Dragon (what I use, better security features and no phone home to Google) Chromium, SWIron, and Opera which my oldest boy swears is the greatest thing ever (hates the new version, went back to using presto) and on the gecko side there is PaleMoon (the other browser I use, I prefer the UI over IceDragon and it seems snappier), SeaMonkey, IceDragon, if you need really low resource there is always Kmeleon which runs really well even on a P3 running Win98SE and if you want to avoid BOTH the Chromium and Gecko engines you can go with QTWeb which is just what it says on the tin, a cross platform browser that uses Webkit and the QT framework...quite nice actually and of course Safari if you are into Apple.
I was using FF before it was called Firefox, and the Suite before that and....yeah, its just not very nice now. The UI feels like a bad Chrome ripoff and it still has "senior moments" where the entire UI can just "hang" for several seconds, which when you have 8 fricking cores and 16GB of RAM? is just inexcusable. I don't know what went wrong with Moz, but for the past few years they seem to have gone out of their way to just ruin the browser, do they no longer care? Has the UI team been taken over by Google? All I know is If I wanted Chrome I'd use Chrome and the current FF feels like a really bad Chrome knockoff, its the "Hipad" that looks kinda sorta like the real thing but once you use it? Yeah its just a knock off.