Found in

• 105.0b7

Affected versions

• 106.0a1 (20220906213903)
• 105.0b8 (20220906185728)

Tested platforms

• Affected platforms:
• macOS 11
• Windows 10x64

Steps to reproduce

1. Open https://archive.ph/uE3pB and pinch zoom the page.
2. Pan down on the page in small increments and observe the scroll behavior.

Expected result

• Scrolling works as expected.

Actual result

• On macOS the scrolling randomly stops while panning and bounces up a little and needs to pan again. On Windows, the panning does not work on the first attempt.

Regression range

• This is not a regression. This was introduced with the pinch zoom feature. Bisected to Firefox 71.0a1 (2019-09-02) with apz.allow_zooming is set on true and the same behavior can be seen.

Additional notes

• Attached a screen recording: link. The behavior can be seen better starting with 00:48 minutes when the scroll is bouncing sometimes toward the end of the video.
• Firefox 104.0.2 and 102.2.0esr are affected by bug 1782339.

Thanks for filing. Just to confirm, the issue does not occur if the page is not pinch-zoomed in at the beginning?

(If so, then I misunderstood what the issue is in bug 1782339 comment 42, since the issue I describe there occurs with or without pinch zooming.)

(In reply to Botond Ballo [:botond] from comment #1)

Thanks for filing. Just to confirm, the issue does not occur if the page is not pinch-zoomed in at the beginning?

(If so, then I misunderstood what the issue is in bug 1782339 comment 42, since the issue I describe there occurs with or without pinch zooming.)

Yup, that is correct. I cannot reproduce this issue if the page is not pinch-zoomed in at the beginning. I can only reproduce the issue that is described in comment 42 without pinch zoom (scrolling stops only when the subframe is maximum-scrolled).

When the page is pinched-zoomed in at the beginning this issue randomly happens even after the subframe is maximum-scrolled while keeping to pan down.
Also, I can only see this issue only while panning down on the page. I cannot seem to reproduce this when I pan from the bottom of the page to the top.

I am able to reproduce this. Doesn't happen very often, but does happen.

Thanks for the clarification. After further testing, I can reproduce this on Linux as well (like you said, only when scrolling downward, not upward), and I agree this is unexpected behaviour.

Just tried to reproduce on macOS -- I can reproduce -- but I noted this: the page has an inner scrollframe which has scroll synced somehow to the window scrollframe. This is visually evident on macOS with the preference set System Preferences -> General -> Show scroll bars: when scrolling. If the cursor is over the inner scrollframe, then I can reproduce the bug. If the cursor is in the margin area -- not over the scroll frame -- then scrolling happens correctly every time.