It would be complicated due to Mozilla's structure. Mozilla Foundation is a non-profit that owns the for-profit Mozilla Corporation. You can donate to the foundation but they can't use the money for Firefox.
But the fundamental reason is that donations are only ever going to be a drop in the ocean. Google gives them $400m/year. Mozilla Foundation donations are like $3m/year. Even Wikipedia donations are only about $100m/year and they have way more users and push really hard.
Probably nothing, but again I suspect they don't bother because it would be a drop in the ocean and certainly not worth the "Mozilla is selling out!" backlash you'd get from the sort of people that use Firefox.
I was of the impression that Mozilla had shed their side projects in the face of dwindling money from Google. Is that still not the case?
I am willing to donate to Mozilla in spite of their mismanagement given that we are creeping ever closer to another browser monopoly. Ignoring bad financial decisions, Firefox is a good product and I've been using it exclusively on PC since Quantum came out. I feel that people here hold Mozilla to some impossibly high standards and turn it into outrage porn. I mean, I don't see top-ranked comments on HN about threatening to stop using Chrome because of whatever sleazy thing Google did last.
But the fundamental reason is that donations are only ever going to be a drop in the ocean. Google gives them $400m/year. Mozilla Foundation donations are like $3m/year. Even Wikipedia donations are only about $100m/year and they have way more users and push really hard.