Keeping that thingy running all those years and making sure it is still competitive against Chrome (that has 1000 times the resources + free access to put ads for their browser on two of the highest value ad spots that exists) is an engineering masterpiece as well as a marketing masterpiece if you ask me.

Also you write like Firefox extensions haven't been years ahead of competition (proven by the fact that no other browsers have even come close even Mozilla had proven what was possible) and like tabs where commonplace in browsers before Firefox.