With pinch zooming, the visual viewport is what more accurately represents the user-visible scroll position, so the session store should update the scroll position as soon the visual viewport changes, not just on layout viewport scrolls. In principle this affects Desktop as well, although in practice this only matters with pinch zooming. I'm going to try change both implementations anyway, though.

Cool, thanks! The idea is for Desktop to eventually get pinch-zooming as well (activated e.g. via the trackpad), so implementing things like this for Desktop as well will come in useful.

Jan is this something you're working on for 64? 65? Geckoview related?

Once I've done bug 1478776, and no, this particular bit doesn't affect the current Geckoview implementation.

CCing Sean for awareness, as the Layout team is currently doing some viewport work.

CC rhunt and hiro in case this is relevant to scroll anchoring (bug 1305957) in any way (or vice-versa)

(In reply to Jan Henning [:JanH] from comment #3) > Once I've done bug 1478776, and no, this particular bit doesn't affect the > current Geckoview implementation. While GeckoView doesn't have anything like the current session store implementation, it does expose scroll events to Android consumers [1] and this might be another case where scrolls of the visual viewport might be the more interesting thing? [1] https://dxr.mozilla.org/mozilla-central/rev/237e4c0633fda8e227b2ab3ab57e417c980a2811/mobile/android/chrome/geckoview/GeckoViewScrollChild.js#29