It's long past time for a consortium of people who care about the web to do what the founders of the Document Foundation did with OpenOffice;
1) fork the codebases Mozilla stewards
2) assemble funding from diverse sources to support their ongoing development
3) hire ex-Mozilla developers who have experience with the forked codebases
Particularly those who quit on principle, in response to one of the many unprincipled decisions at Mozilla Inc. (eg nonfree DME module from Adobe).