The problem with Mozilla is not just technical but cultural. The organization has been infected with managers. The managers want to keep their jobs more than they want Firefox to succeed. Clearly the solution is for the managers to fire themselves and allow the developers to run the show, but that was not going to happen.
Ladybird, by contrast, is a developer-lead open source project that has no such constraints. They also don't have a product yet but I'm sure the picture will be radically different in a few years.
Conway's law in action.
> The problem with Mozilla is not just technical but cultural.
Not once in my career have I come across a problem that wasn't cultural. There are no purely technical problems in software. Everything can be achieved, everything can be worked around. All one need is a consensus. Enters cultural problems.
> The managers want to keep their jobs more than they want Firefox to succeed.
Coincidentally, also throughout my career, not once have I met an engineer that didn't put the entire blame on managers. Introspection really isn't our forte, is it? :)