User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:87.0) Gecko/20100101 Firefox/87.0

Steps to reproduce:

Changed the windows resolution scale from 100% to 125% or 150% on my TV screen.
The resolution of my TV is 1920x1080, same as my monitor (primary screen).
The native resolution is 1920x1080.

1. Turn off the Smooth Scrolling from settings.
2. Disable the WebRender to switch to DX11 with webrender.force-disable
3. To to YouTube (https://www.youtube.com/watch?v=q9NB5PUOFh4) and scroll down
4. Now scroll up. The images that are out of the View Box and when rendering on the screen are moved down 1px. After scrolling down again, the images are moved up again (Same if is half out of the screen)

Actual results:

https://drive.google.com/file/d/1sggGOCRJjEA8133BnA4JgOxp9nKgGRLI/view?usp=sharing

The Bugbug bot thinks this bug should belong to the 'Core::Graphics: WebRender' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Not WebRender. Disable it with webrender.force-disable = true.

I think this is the same with the GitHub icons?
And I found same thing but not know what the website was.

After scrolling down and again up the Icons are centered vertically correctly.
After moving the mouse over them, all icons are moving down a bit.

Also compared to WebRender, the icons remain down, but are not centered vertically correctly.

Same on the https://www.youtube.com/feed/subscriptions - Zoom to 150%, use the Page Down to scroll some down and Page Up to see.

Can you make a reduced testcase or use mozregression to find a regression range?

I will try later to see what I can find. Need to sleep a little.

Where what I found. Can you check check them?

Good:
app_name: firefox
build_date: 2020-10-03 09:17:56.774000
build_file: C:\Users\Marian.mozilla\mozregression\persist\cab81767be70--autoland--target.zip
build_type: integration
build_url: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/Mp3nI7nlQlaKscM4cKQhaw/runs/0/artifacts/public%2Fbuild%2Ftarget.zip
changeset: cab81767be70469b780cd372ff463df59c2264e0
pushlog_url: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=cab81767be70469b780cd372ff463df59c2264e0&tochange=4f3c9c44c1f9cba7b821cb3b8254a41cbbf3bf44
repo_name: autoland
repo_url: https://hg.mozilla.org/integration/autoland
task_id: Mp3nI7nlQlaKscM4cKQhaw

Bad:
app_name: firefox
build_date: 2020-10-03 10:43:02.660000
build_file: C:\Users\Marian.mozilla\mozregression\persist\32a2e59ab726-pgo--autoland--target.zip
build_type: integration
build_url: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/CpfRFyziQXGsZ1YdqUIzJA/runs/0/artifacts/public%2Fbuild%2Ftarget.zip
changeset: 32a2e59ab7260118d8d5f430e503967fad6993cf
pushlog_url: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=cab81767be70469b780cd372ff463df59c2264e0&tochange=32a2e59ab7260118d8d5f430e503967fad6993cf
repo_name: autoland
repo_url: https://hg.mozilla.org/integration/autoland
task_id: CpfRFyziQXGsZ1YdqUIzJA

The log is on the file.

Really hard to record the behavior. Here is a better video.

About the icons are moving on the first video, seams to be other regression.

Thanks for that! Very useful!

Can you try setting apz.force_disable_desktop_zooming_scrollbars to true in about:config and see if that fixes the problem? (This isn't intended as a fix as we don't want to run with that setting long term but it will help us investigate and hopefully fix the issue.)

Yes. Works fine with it to True.

Thanks for testing. I might have further questions about your configuration so I can try to reproduce myself.

Here some information, ask if you need more:

Windows 10 1809 / Linux Mint 20.1 Cinnamon
CPU: I5-4449 @ 3.1GHz x 4
GPU: Intel HD 4600
MoBo: GA-H87-HD3
RAM: 8GB
Monitor: Philips 226V4L 1920x1080

Windows Composting: DirectX 11
Linux Composting: Basic

i5-4440 ...

Would you be able to run mozregression while setting the pref apz.force_disable_desktop_zooming_scrollbars to false in mozregression? I can help you with this part if you need. This would tell me which part of the code that landed behind that pref caused the problem.

Bad:
app_name: firefox
build_date: 2020-08-06 09:18:13.994000
build_file: C:\Users\Marian.mozilla\mozregression\persist\a09e4ce9ebba--autoland--target.zip
build_type: integration
build_url: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/fQyRPbD1RPKUJLwhw-mY1A/runs/0/artifacts/public%2Fbuild%2Ftarget.zip
changeset: a09e4ce9ebba8fa4a29a4833560c8ee807018c03
pushlog_url: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e2337fd0fe7718a26d9ea0601fc4004a7b8ff586&tochange=a09e4ce9ebba8fa4a29a4833560c8ee807018c03
repo_name: autoland
repo_url: https://hg.mozilla.org/integration/autoland
task_id: fQyRPbD1RPKUJLwhw-mY1A

Good:
app_name: firefox
build_date: 2020-08-06 09:15:28.008000
build_file: C:\Users\Marian.mozilla\mozregression\persist\a518405abe4c--autoland--target.zip
build_type: integration
build_url: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/Mr3D_QNWSVKG7jMVyzQewQ/runs/0/artifacts/public%2Fbuild%2Ftarget.zip
changeset: a518405abe4c93e6d8df622f59d5f01c4766e1d5
pushlog_url: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a518405abe4c93e6d8df622f59d5f01c4766e1d5&tochange=a09e4ce9ebba8fa4a29a4833560c8ee807018c03
repo_name: autoland
repo_url: https://hg.mozilla.org/integration/autoland
task_id: Mr3D_QNWSVKG7jMVyzQewQ

Result:
Bug 1620055 - Turn on allow_zooming on nightly desktop builds. r=ktaeleman

Differential Revision: https://phabricator.services.mozilla.com/D85432

2021-07-08T20:12:08.297000: DEBUG : Did not find a branch, checking all integration branches
2021-07-08T20:12:08.297000: INFO : The bisection is done.
2021-07-08T20:12:08.297000: INFO : Stopped

Other difference between that builds is that the Bad one still has SmoothScroll for PageUP and PageDown if the smooth scroll is disabled.