Most of the Firefox alternatives are standards-compliant also (specifically, the two big ones definitely are). And I don't see as many rendering regressions with them as I do with Firefox. So who truly benefits if I devote my team's engineering resources to chasing down Mozilla's bugs?

There might be some benefits to an engine multiculture; with so many engines derived from Chromium or Webkit, one could make a technical argument that maintaining Gecko as third choice has merit. I find that argument to be weak. Gecko has been around for longer than the other two and it isn't remarkably better (and seems to fall on its face quite often relative to alternatives). What if it's just a tech stack whose time has come and gone? How many resources are we wasting propping up an old stack that could be used to build, perhaps, a fourth option? Or solve existing problems in the other two? There's this vague hand-wavy assumption that Firefox represents "the open way of doing things" (odd when it's also maintained by a corporation, like the alternatives), but I don't see it as particularly more open than the other options.

I don't think I'm doing a disservice to the community by refraining from using jQuery and I don't think I'm doing a disservice to the community by refraining from going out of our way to support Firefox.