> Make the browser development the charitable work
They probably cannot do this. The IRS generally does not consider writing open source software to meet the requirements of a 501c3, for example [1]. They aren't super consistent about it so some groups have gotten 501c3 exemption in the past, but for the most part there is a reason that 501c3 open source foundations focus on support activities, conferences, and not software development.
> accept funding to non-charitable company
They could do this, just like they did for Thunderbird, and I wish they would.
[1] https://www.mill.law/blog/more-501c3-rejections-open-source-...