I've noticed this fairly recently, though it's reproducible on release, so I suspect it's not a recent regression. Str: * Go to https://amp.slate.com/business/2018/12/google-walkout-protests-contract-workers.html?via=gdpr-consent (just a random twitter link I happened to click on) * Scroll down to the article content enough so that the address bar disappears. * Scroll up. Expected: no jumps Actual: the scroll position jumps significantly enough to be annoying :) I'm not sure of which component this should be in, so trying APZ for now... Though its not reproducible with Geckoview on focus, so it may be a front-end issue instead? I've seen other websites with this behavior but not all of them, I can find more links if needed / wanted. It also happens when scrolling diagonally on this page fwiw.

I think apz is the right component since it seems to jump on the main-thread repaint that happens after async-crolling.

It looks like it might be JS on the site reacting to a resize of the browser window, which happens when the dynamic toolbar transitions on or off screen. I'm not sure how Focus's dynamic toolbar works, but I know it doesn't use the same code as Fennec's so it could well be doing something differently.

(In reply to Botond Ballo [:botond] from comment #2) > It looks like it might be JS on the site reacting to a resize of the browser > window, which happens when the dynamic toolbar transitions on or off screen. > > I'm not sure how Focus's dynamic toolbar works, but I know it doesn't use > the same code as Fennec's so it could well be doing something differently. Talked to :snorp today and he confirmed that Focus's dynamic toolbar does not resize the viewport. When the toolbar is shown, a corresponding slice of the bottom of the viewport is just offscreen (so elements fixed to the bottom might be cut off or hidden altogether). So yeah, pretty sure this is related to web content reacting to resizes. May not be much we can do about it (though if it doesn't happen in Chrome, it would be good to understand why).

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