1204967 - Everything twitches if I autoscroll web page on zoom level < 100%

Status: NEW

(Core :: Layout, defect)

Description

[arni2033]

Attachment: video - Everything twitches if I autoscroll web page on zoom level is less than 100percent.webm

STR:   (Win7_64, Nightly 43, 32bit, ID 20150913030204, new profile, safe mode)
0. Set pref   layout.css.devPixelsPerPx -> 1.0   (because on HiDPI it reproducible for another number than 100% - less than 100%)
1. Open https://en.wikipedia.org/wiki/Shadow_Raiders (in fact any page exposes this behavior)
2. Reduce zoom level so that it was < 100% (e.g. 70%)
3. Click middle mouse on free space on page to start autoscrolling
4. Move mouse 1-5px below the autoscroll circle

Result:       Everything is twitching. This is safe mode.
Expectations: Page elements shouldn't move relative to each other.

Comment 1

[Paul Oiegas [:poiegas], PM for Ecosystem QA (OMC, New Tab, Contextual, Nimbus, Experiments), Services QA (VPN, FxA/Subplat, Relay, Monitor), WebCompat QA, and Solo QA teams)]

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0

Managed to reproduce this in normal conditions (safe mode is not mandatory) on latest Nightly (45.0a1) with the above mentioned steps. Updating the issue component.

Comment 2

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

I think this is just rounding changes in the positioning of elements. 70% is going to result in fractional numbers when positioning. Moving to layout.