I think they need to integrate better with their paid offerings to build additional revenue streams. For example, Mozilla VPN works with Container Tabs, but I had to look for it; that's a pretty killer feature IMO. Make it work on mobile too and a lot of people would be interested. Maybe they could white label a password manager (Bitwarden?) as an alternative to their built-in PW manager service, and make the experience really good. Throw in Relay as well.
There's a lot they could do with opt-in, privacy-centric features that I would be totally interested in.