"donations amount to so little" is very misleading stated like that because Mozilla just doesn't give us any way to donate to Firefox development or even just their FOSS efforts in general. Mozilla is one of the very few companies I've donated to even when I had little in the way of discretionary income, and is one of the first options people think of when they think of FOSS software they want to donate to. But then I learnt that any donations like this are highly unlikely to be spent on the software we're donating it for, and at that point I might as well donate to a random local charity instead.

I'm not gonna claim that donations would have rivaled the Google revenue otherwise, but they will certainly be many many times higher than what they are. Lots of people are willing to and even want to set up a regular donation to Firefox as the lone non-Chrome bulwark in the FOSS space. There would have been grassroots efforts to get more people to donate on the regular, hell I would have put in serious work on such efforts if we actually had a way to donate to keep Firefox alive and healthy.