> how to pay for that

I would not mind to pay for the browser, but they will not let me.

This is a consequence of browser monopolies, established by Microsoft in the 90s: everyone should have to pay for a browser and make a deliberate choice in vendor. The fact that they're free and subsidized by large businesses in other markets, rather than being a product you choose to buy, is a concrete example of monopolistic market distortion.

You say that, but out of the remaining users of FF, I severely doubt even 1% would pay. Any attempt to paywall would kill whatever they have left.