As minor counterpoint: Firefox is not strictly speaking developed "by Mozilla" but by the community. Mozilla's the curator, and has a fair bit of staff also working on it, but vast swathes of the codebase are community contributions. If you need FF to do a thing, and you think you have good enough ideas to contribute the solution there, then rather than upvoting a bug, or bumping it to ask what's happening, be the person to make the happening happen =)
Of course, but bug upvotes don't hurt that cause, either. I have a few reasons that I work on open source projects. First, to fix a bug or add a feature that affects me directly. Second, to learn something new. If I'm just doing the latter, I'd prefer to tackle a bug with more interest/votes, to help others out while I'm at it and increase the odds of finding a willing reviewer.
I doubt it'll happen anytime too soon, but Mozilla should see the community interest.