Even the linked ghostty PR on your home shows this - this is Firefox Android on a Nokia XR21 / TA-1486.

It's not unuseable, but it definitely feels like 'js hacking my scrolling' and not a native surface flinging around.

The experience is actually worse with smaller movements, i guess because my brain is more conscious when breaking the 'finger physically moving the text' illusion.

I don't mean to be dismissive - you're working on a really hard problem, and you're clearly approaching it with a mindset of perfection. I'm posting because I know you're probably able to solve this too :)

Edit: as a point of (unfair) comparison, the codemirror Huge File demo works fine: https://codemirror.net/examples/million/ It does suffer from the occasional partial paint when quickly coasting, but I'm not bothered by this at all, it's far less intrusive than dropping frames / stuttering / etc.

Maybe i need to buy one of these devices to test.

Just to be clear tho, we don't actually scroll jack, native scrolling works as it should and content should move with normal gpu composited scroll. That said, it's possible that loading that much data into memory may be causing causing knock on effects somehow that are just slowing everything down.