It's not like changing wording for 3rd world nations at all (In fact, that usage is, AFAIK, mostly colloquial, the term was designed for other things, and there are other terms that say more and describe things more).
Master and Slave are technical terms, and I've used them before, if you've done any amount of programming, chances you have too. And just describing them as such doesn't sound so awkward, but when you're describing the operation, it does get pretty awkward, and there is little reason to keep it. Standards vary from company to company, from language to language, documentation to documentation. I think some people fail to understand just how unimportant this is. Programmers change variable names all the time, even more often poor ones who can't be bothered adhering to some sort of standard. It's an old term, and they die.
Mozilla does run on donations, but those donations do actually pay for things and people. There is surely a far greater amount being spent on many more things that you personally do not use or care for. Picking this one says more about the person who takes issue with it than Mozilla. But of course, feel free to not donate, not that it's particularly likely that most people are. What Mozilla does run on, for the greatest part, is the goodwill of other developers who work with them, and they've made it clear in the past that they have an interest in supporting diversity amongst programmers. Yeah, that does mean making things more welcoming to people of all stripes, because innovation can and does come from anywhere, and the only person who believes otherwise is simply a bigot. If you don't want to pay for it don't, but the peanut gallery is just petty.