1000% this. i was literally writing the same comment. just have an easy way for me to selectively donate $15/month to Rust, Servo, Firefox, Thunderbird, whatever. instead you get some generic bucket with no possibility to really vote with your money.
e.g. i would have never paid for the A/R stuff they distracted their Servo engineers with (plus the Magic Leap entanglement). i would have also withheld funding for the non-removable Pocket integration fiasco. and the jack-in-the-box Mr. Robot promotion - once my tools start to become Mozilla's agents rather then user's agents, they cease to be my tools.
i should add that people who choose to use firefox rather than the default are those who are most likely to pay. not listening to them is absolute nonsense.