Affected versions

• Firefox 69.0b8 (20190723212625)
• Firefox 70.0a1 (20190724220024)

Affected platforms

• Ubuntu 16.04
• macOS 10.14
• Windows 10x64

Steps to reproduce

1. Launch Firefox and go to http://lembarsaham.com/.
2. Using the mouse wheel scroll to the bottom of the page and then scroll back up.
3. Hit the arrow down button from the keyboard.
4. Try to scroll again using mouse scroll, auto-scroll or dragging the scroll bar (if the issue is not reproducing repeat step 2 and step 3).

Expected result

• The page is scrolled accordingly.

Actual result

• Cannot scroll the page with methods from step 4.

Regression Range

• Potential regressor bug 1543599.

Additional Notes

• After the scroll is locked the page can be scrolled only from the keyboard.
• Using scroll to top button from the webpage fixes the issue.
• Note that the issue is intermittent. From what I see on Nightly, steps 2 and 3 have to be repeated several times.
• Attached a screen recording with the issue.

Could you find a real regression range? Though it seems I can repro something similar with layout.css.scroll-anchoring.enabled=false, so it's probably not a regression from that bug.

(In reply to Emilio Cobos Álvarez (:emilio) from comment #1)

Could you find a real regression range? Though it seems I can repro something similar with layout.css.scroll-anchoring.enabled=false, so it's probably not a regression from that bug.

Hello Emilio,
Unfortunately, I cannot reproduce the bug with layout.css.scroll-anchoring.enabled=false. Can you give me some STR how to reproduce it? And can you tell me what AR is there when it's reproduced?

When searching for a regression range with layout.css.scroll-anchoring.enabled;true I've managed to reproduce the bug until Firefox 66.0a1 (20190111215452). The builds under this one don't have this pref.

I attached a screen recording: link with the behavior which includes bug 1543599. The steps I use in the recording are:

1. Scroll down with the mouse wheel until the page automatically scrolls.
2. Use down arrow key multiple times.
   AR: Cannot scroll using the mouse wheel, auto-scroll or dragging the scroll bar.

I think that is the same behavior encountered in this bug. Sorry for any confusion created because I assumed that bug 1543599 is the potential regressor.

Ok, so this is not a regression from bug 1543599 as comment 0 seemed to imply. Bug 1568778 will probably help here.

Hi Alexandru, are things working better now that bug 1568778 has landed?

(In reply to Ryan VanderMeulen [:RyanVM] from comment #4)

Hi Alexandru, are things working better now that bug 1568778 has landed?

Hello Ryan,
Using Firefox 70.0a1 (20190731215544) on Windows 10x64 I cannot reproduce the issue following the steps from comment 0. Tried several times with different scrolling methods.

Hello!
The issue is verified fixed using Firefox 70.0a1 on Windows 10x64, macOS 10.14 and Ubuntu 18.04.