1498920 - On a really long bmo page, selecting text+ fast scrolling will make the scrollbar jump

Status: RESOLVED WORKSFORME

(Core :: Graphics: WebRender, defect, P5)

Description

[Mayank Bansal]

Attachment: bandicam 2018-10-14 21-00-21-026.mp4

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0

Steps to reproduce:

Create fresh profile. Enable WR

1. Go to areally long bmo page like https://bugzilla.mozilla.org/page.cgi?id=user_activity.html&action=run&from=-14d&who=sledru%40mozilla.com
2. Scroll to the bottom
3. Select all but the last couple of lines of text by doing ctrl+A, and then doing shift+mouse click on last couple of lines
4. Drag the scrollbar to the top of the page very fast
5. (The page will struggle to paint because of slow layout+ table painting)
6. While the page is still checkerboarding, grab the scrollbar and scroll a little
5. 


Actual results:

As soon as you scroll a little down, the scrollbar moves A LOT downward


Expected results:

not so

See video

Comment 1

[Mayank Bansal]

I guess the bug can be restated as :On a long page with tables, when the page is very busy doing table painting, scrollbar can jump a lot when trying to grab by mouse and moving

Comment 2

[Mayank Bansal]

In the video, at the 7-8 second mark, I grab the scrollbar ith mouse, and give it a small downward drag. In response, the scrollbar jumps a lot downward

Comment 3

[Darkspirit]

Debian Testing, KDE, Xorg, GTX1060
This also causes a (never ending?) e10s loading circle if you switch to another tab and back.

Comment 4

[Mayank Bansal]

the never ending spinner is the long table painting /text visibility calculation. See bug 1464632

Comment 5

[Mayank Bansal]

Cant repro this anymore. Closing for now.

Comment 6

[Mayank Bansal]

Sorry, i lied. I tried with a better URL and can still repro.

URL : https://bugzilla.mozilla.org/page.cgi?id=user_activity.html&action=run&who=release-mgmt-account-bot%40mozilla.tld&from=2018-02-22&to=2019-03-08&group=when