The biggest issue with forks, which is pointed out in the article, is Mozilla still does the heavy lifting. None of the forks have the resources (and probably interest) to fully fork Firefox and make it their own codebase to maintain.
Personally, I like LibreWolf and Mullvad browser. Hopefully they can keep up to date well into the future.
These projects to my knowledge do not release patches by themselves but as you said, rely on Mozilla's work - they take Firefox, strip it out of few features - namely one's that raised concerns, toss in additional stuff from other projects and include own branding. So perhaps these are more "customized derivatives" or "spin-offs"?
Not that work of these projects isn't good - on contrary. Mozilla has violated the trust of its users in last years with features nobody ask for and those folks pluck that stuff out.
Stil, perhaps it's a time for a proper fork that provides own code maintenance, before things will go worse at Mozilla.
Personally, I like LibreWolf and Mullvad browser. Hopefully they can keep up to date well into the future.