Google wants what's best for Google, Apple wants what's best for Apple and Microsoft wants what's best for Microsoft. Since all three are grasping multi-national capitalist corporations with a fiduciary duty to shareholders, that's to be expected.
Since "Mozilla is a proudly non-profit organization dedicated to keeping the power of the Web in people’s hands" then it is able to do things differently.
However, users are basically self-interested and short sighted (basically "how fast does a tab load") so just being morally superior isn't a win ;-)
Exactly, being morally superior gets you no where, and being morally inferior doesn't hurt you either. You said yourself that users only care about "how fast a tab loads." Well, if Google ships a browser that's terrible, people will switch to something else. That's why competition still exists! Firefox was in a position to dominate the desktop browser market, but then Chrome came alone and ate their lunch! There's nothing stopping Mozilla from regaining that market share, but they're going to have to ship a better browser!
Partly tongue in cheek. However, we know that Google, Apple and Microsoft will do what is best for their companies, however they dress it up. Mozilla, being non-profit, does have a better ideological foundation for doing what is best for the web.
Of course, it does come down to individuals in the end, and
open source has pointless turf-wars, so nothing is guaranteed....