Make Firefox fully and exclusively a tool in service of the user.
Eliminate - both in code and by policy - anything that compromises privacy. If a new feature or support of a new technology reduces privacy, make it optional. Give me a switch to turn it off.
Stop opting the user into things. No more experiments. No more changing of preferences or behavior during upgrade.
Give the user more control; more opportunities for easy and powerful automation and integration.
Not only would this win me back as a user, I'd pay for the privilege. I'm paying for Kagi and happy to be doing so. I'd love to pay for an open source browser I could trust and respect.