> What would "Foxium" offer that Brave, Vivaldi, Edge, Chromium, or Chrome don't already offer?

More ability, at any given cost, to innovate on candidate new web technologies maintaining Mozilla’s objectives to promote the open internet, acheived through lower cost to implement and maintain consensus technologies.

Which is similar to what other Chromium-descended third-party browsers offer their sponsoring entities, but each sponsoring entity has different objectives. Everyone benefits from the ability a common open-source core provided to distribute (or just outsource) the cost of maintaining the features that are shared, leaving more bang for engineering buck on each entity’s investment in not-yet shared features.

Which isn't to say that diversity in implementation of the shared features doesn't have its own benefits to the ecosystem, particularly in terms of preventing future development from being adversely constrained by what is practical to bolt on to one particular implementation without rewriting big parts of the core. But, for that to really bear fruit, you'd need more diversity than the existing Blink + WebKit + Firefox ecosystem provides anyway, and it's not like Mozilla can conjure that out of thin air.

Those are all fair points, but if Firefox has a hard time driving adoption now, I think being on Chromium they'll find it even harder, unless they have some real killer, must-have features lined up. But I doubt they have those features planned because if they would use them to drive adoption in Firefox now.