1327654 - [HiDPI] Black vertical line briefly appears between elements on VK.com when I switch to next image

Status: NEW

(Core :: Layout, defect, P3)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 49, 32bit, ID 20160526082509
STR_1:
0. Set DPI -> 125% :
 A) Set DPI level -> 125% in your OS   [OR]
 B) Set layout.css.devPixelsPerPx -> 1.25
1. Open https://vk.com/wall-7736865_418381
2. Click on the 1st image
3. Repeat 10 times: {press Left key, wait 1s}

AR:
 All images 6, 4, 1 all briefly display 0.5px black vertical line between
 image and the (empty) comment section at the right, but after 0.1s the black line disappears

ER:  Either X or Y for each image.  Don't know what's correct here; it depends on layout of each image
 X) image should display the black line constantly, when I open it
 Y) NO BLACK LINES: image should NOT display the black line at all, when I open it

Comment 1

[Vlad Bacia-Mociran [:VladB]]

User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:53.0) Gecko/20100101 Firefox/53.0

I have verified this issue on Windows 8.1 x64 with latest Nightly (Build ID: 20170116030326) and latest Firefox release v50.1.0 and it is reproducible. 

After step 2 from comment 0, I have opened the Web Console and inspected the whole layout with the detailed picture. While inspecting the layer I have cycled through all the pictured using the arrows from keyboard and observed that the margin-top is dynamically allocated depending on the viewed picture but gets stuck at the most lower value.