I think you're misunderstanding my point, it's not about implementation or spec bugs but design. Forget Ladybird for a moment and think of Firefox. Its core design was something along the lines of 'x-platform toolkit for making enterprise groupware apps' where one of the apps was a web browser. Kind of neat for 1998, by 2008 it was clear that's no longer a good fit for making a browser. Despite heroic efforts and many advances, Firefox has never really been able to close the gap to more recent browsers. And (statistically) nobody makes new browsers based on Firefox, it's effectively a design dead end.
It can be hard to retrofit 'complicated but decent parser with a js runtime attached' to something like 'safe parser of arbitrarily adversarial inputs connected to an open RCE' (i.e. something akin to a modern browser) if the latter wasn't a fundamental design goal to start with.
It can be hard to retrofit 'complicated but decent parser with a js runtime attached' to something like 'safe parser of arbitrarily adversarial inputs connected to an open RCE' (i.e. something akin to a modern browser) if the latter wasn't a fundamental design goal to start with.