Sure: pay money directly to one of a thousand developers to implement missing functionality or fix pressing bugs in Firefox and make a pull request on it.
For example: I see that Firefox still hasn't yet made all SVG elements attributes into presentation attributes per the SVG 2 spec. So right now in Firefox you can't do 'rect.style.width = "12px"' but in Chrome you can.
Not sure you could easily get full coverage (e.g., I'd bet css "d" atty would be tricky). But there's probably a fairly workable introductory subset for which one could create a fairly clean patch set.
Or pick a different self-contained, non-controversial feature/bug and fund a dev to attack it.
I'm sure that funding for "a tiny feature" or fixing "one tiny bug" would be beyond what most users can pay for at an individual level and still have the developer make a decent living. All the work that's desired to be done needs collective donations to be pooled and used since individual donations would be very small by nature.
Your suggesting feels good at a personal connection scale (i.e. you fixed my bug painpoint, have some dosh), but really to get the sort of traction where the donations are viable you'd be working at a much larger scale right? Plus, why should the donator does each do this all headwork? Charities make it easy to donate for a reason, it increases donations... Specifically on the topic of scale, if the donations are small enough to not run into this problem, they are probably too little to impact anything, hence scale matters if the donations do.
Hell, just start by filtering the open bugs for stale pull requests. Find the handful that look relatively self-contained and get in touch with the dev who wrote the patch and go from there. A lot of times they just assumed nobody gave a shit and will quickly revise the patch if there was a problem with it.
Better yet-- buy a few meals for a dev to write a tool to generate this data for you.
For example: I see that Firefox still hasn't yet made all SVG elements attributes into presentation attributes per the SVG 2 spec. So right now in Firefox you can't do 'rect.style.width = "12px"' but in Chrome you can.
Not sure you could easily get full coverage (e.g., I'd bet css "d" atty would be tricky). But there's probably a fairly workable introductory subset for which one could create a fairly clean patch set.
Or pick a different self-contained, non-controversial feature/bug and fund a dev to attack it.