If by "people" I mean everyone and not just direct users of their products. Something more akin to the Linux or Apache Foundations, including both private sector donations and government grants etc. A DIVERSE set of funding sources, not sharing ad revenue from a direct competitor. Having "people" directly pay to play as it were would never work, as we've seen before in other industries like news, etc.

The private sector has no need for Firefox. Government grants are better spent elsewhere.

Many companies and governments have a vested interest in the web continuing to exist as an open platform and not just a corporate playground controlled by 3 corporations. Without Firefox or something like it, the web becomes a defacto standard at best, largely controlled by Google (and to a lesser extent Apple and even lesser extent Microsoft)