How can I donate some money that is specifically for Firefox development?
I do not really care for or like the other products that Mozilla is developing, like VPNs etc but rather, I would like for my money to be used towards browser development.
Exactly. Somebody should organize a fund for that, add an easy subscription solution, like Patreon, make it widely known, and sort out all the legal and tax issues.
(Unfortunately, I don't see myself doing that. At least not yet.)