You can't fight for an open web just by making a browser. As dire as the Firefox market share is today, it'd be so much worse if the Foundation didn't spend its time and effort making sure the folks who don't give a shit, but should (e.g. politicians, law makers, lobbyists, news outlets, etc. etc.) learn why they should give a shit about the open web.
It sucks that you can't donate to Firefox directly, but calling what the foundation does "irrelevant" feels like you're not looking at the very real big picture of everyone wanting to lock down the web, all the time, everywhere.