[Affected versions]:

• 66.0b9
• 66.0a1 (2019-02-20)

[Affected platforms]:

• Win 10 x64
• Ubuntu 18 x64
• macOS 10.13

[Steps to reproduce]:

1. Go to https://forum.gaijinpot.com/forum/community-center/general-discussion
2. Reduce the width of the browser to or less than 497px
3. Scroll the page using the navigation keyboards or the up-down arrow buttons on the scrollbar.

[Expected result]:

• Scrolling is performed smoothly.

[Actual result]:

• Scrolling action is barely noticeable.

[Regression range]:

• Last good revision: f8b8346df03cfd7d683faf16ddded0afd528570b
• First bad revision: 893f2ec05d7acf999174e200b042c3c9ef6fdd7c
• Pushlog:
  https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=f8b8346df03cfd7d683faf16ddded0afd528570b&tochange=893f2ec05d7acf999174e200b042c3c9ef6fdd7

[Additional Notes]:

• With the layout.css.scroll-anchoring.enabled on false, this issue is not reproducible.

I see the same bad results in Chrome, too. So this seems likely to be a legitimate interaction issue caused by the Scroll Anchoring feature, regardless of browser.

rhunt, perhaps you could take a look at what's causing trouble here & whether there's anything obvious we could fix to avoid it?

Bulk change to wontfix for 68 (P3+ carryover with needinfo).

I won't have time to look at this anytime soon, unfortunately.

I think this is fixed now, mind confirming?

This issue is no longer reproducible with the latest Nightly 70.0a1 (2019-07-25) and Beta 69.0b8 on Windows 10, macOS 10.13 and Ubuntu 18.04.