The core will have to still be a solid battle tested thing. Imagine having to worry about if your vibed browser is quietly dropping some elements. Firefox and Chromium browsers are valuable because they are the targets, if a site doesn't render properly in them, it can be said that the site is wrong.

If everyone runs a vibe coded browser engine that evaporates and you might as well just have sites serve a bunch of markdown for LLMs to render in whatever inconsistent way they choose.

Vibe coding is obviously not quite there yet right now. But in the future it will be. The output of agents will be just as correct and rock solid as the software from the most experienced software developers. We'll also have the additional advantage of there being existing browsers to use as an oracle to test against to ensure that nothing regresses.