1524170 - Scroll position is different after rotating from portrait to landscape

Status: UNCONFIRMED

(Core :: Panning and Zooming, defect, P3)

Description

[csheany]

User Agent: Mozilla/5.0 (Android 7.1.1; Tablet; rv:67.0) Gecko/67.0 Firefox/67.0

Steps to reproduce:

1. Open https://github.com/mozilla-mobile
2. Request desktop site
3. Scroll to the bottom
4. Rotate to landscape

Actual results:

The middle of the page is in view.

Expected results:

The bottom of the page is in view.

Comment 1

[Botond Ballo [:botond]]

Scroll position not being preserved across rotations is a long-standing known issue.

The reason for it is that the representation of the scroll position that's preserved across the rotation is a numerical offset in pixels. When the device is rotated, the page content is laid out into a different width, and as a result there can be different content at the same numerical offset.

There is a new spec called Scroll Anchoring [1] that's intended to address issues like this. It was recently implemented in Firefox, and I believe it's enabled in Nightly. Perhaps Ryan can comment on why it's not kicking in for this website.

[1] https://drafts.csswg.org/css-scroll-anchoring/