1355372 - Scrollbar jumps by 1px after the page changes scrollTop

Status: NEW

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

Description

[684sigma]

Attachment: scrollbar jumps by 1px, by reporter.html

I have a problem with Firefox Beta 53. It also happens in Nightly 55. Doesn't happen in ESR 45
After scrolling in scrollable areas on some sites, scrollbar jumps by 1px, it's distracting. Here's how to reproduce it:

1. Open attached page
2. Hover mouse over "The long button", wait 2s, move mouse away
3. Hover mouse over "The long button", wait 2s, move mouse away

Result: in one of 2 attempts, scrollbar jumps by 1px after moving mouse away from the button (watch closely)
Expected: scrollbar shouldn't jump

Comment 1

[684sigma]

Mozregression-gui generated this regression range:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=af7c0cb0798f5425d5d344cbaf0ac0ecb1a72a86&tochange=dd1abe874252e507b825a0a4e1063b0e13578288
->
1253860 – Add a lightweight mechanism to update APZ scroll offset without a full repaint
https://bugzilla.mozilla.org/show_bug.cgi?id=1253860
(it's not 100%, but it seems the right bug, because it caused multiple scrolling issues)

Comment 2

[ovidiu boca[:Ovidiu]]

I can reproduce this on Mac OS X 10.10 with FF 52 release and FF Nightly 55.0a1(2017-04-11)

Comment 3

[Ryan VanderMeulen [:RyanVM]]

Too late for a fix for 53. Would consider a low-risk patch for 54 should one materialize. Any thoughts, kats?

Comment 4

[Kartikaya Gupta (email:[e-mail])]

I can repro on OS X and Windows. Didn't verify the regression range but it seems plausible. However it seems like a relatively minor issue so I'm marking it P3.