If anybody is going to pay for a browser it must be better than its competition.
I would pay for better privacy, adblocking, higher speed, better dev tools and what not. But Firefox is not so much better than Chromium in any of these points to warrant payment.
Individually, all their paid offerings aren't that interesting. Scroll, Pocket, and privacy VPN's are all fine little niche products, but bundled together and called Firefox Pro, it gives you vision of what a premium browser might look like: the browser is free, paid users get a collection of services and support the open web.
I vastly prefer Firefox and always did for some reason (I keep testing Opera, Vivalidi, Chromium and what not but none of them clicked with me) but I still see you point, it would be hard for many to justify a high price even if they prefer it.
I'd still happily pay for Firefox (not Mozilla) but I'd consider it an insurance more than an investment at the moment.