It's purely a theoretical, since nobody has offered me a choice of that model - either I'm a source of ad revenue whether I want to be or not (Chrome, FireFox, Safari), or I'm in a captive ecosystem where I'm already paying a premium (Safari, Chrome for android)

I think asking people if they're one of a small of handful people donating into the void to a is a straw man.

Last I checked, you can't donate to fund firefox development.

You can donate to Mozilla, who then go on to spend their money on things other than firefox development. Or development in general.