alt Hacker NewsThere is no precedent for donations on the scale of what Mozilla gets from search licensing. The best online fundraising drive on the planet is Wikipedia with orders of magnitude more users and they don't raise half of what Mozilla spends on keeping up with Google.
It's not the panacea people keep assuming it is, it's just one of many accusations that gets flung at the wall.
Except Thunderbird now does run on donations (though is looking a relevant additional funding sources, e.g. providing hosted email: https://www.tb.pro/en-US/). This is not to say Mozilla can't seek out other sources of money, or develop appropriate ancillary services, but the absence of an option to just give money for Firefox (and Firefox only) is noticeable.