I wonder if anybody else is interested in having it developed. Maybe if a couple of star developers currently being laid off, or redirected to other stuff, started to put more effort into it, and the community started supporting them with donations, that could speed things up?

Firefox is widely popular, and its popularity is also wide among the techs-savvy, well-paid people. Pledging to pay $10/mo for Firefox development would make a difference if, say 20k, or 50k people subscribed. I suspect there is a chance to achieve such numbers with a well-run campaign.