1235834 - [HiDPI] white vertical lines are displayed within a tab when I drag it (on lightweight theme)

Status: NEW

(Core :: Layout, defect)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 46, 32bit, ID 20151223030323

STR:
1. Set DPI -> 125% :
 A) Set that DPI level -> 125% in your OS   [OR]
 B) Set layout.css.devPixelsPerPx -> 1.25
2. Install theme https://addons.mozilla.org/en-US/firefox/addon/just-black/ and enable it
3. Open new window with 2 tabs
4. Hover mouse over the 2nd tab, press left mouse button, move mouse to the right (start drag-n-drop)

Result:       White vertical lines are displayed within a tab
Expectations: There should be no white vertical lines, just like on normal DPI (100%)
 
Note:  I'm not sure if component should be "Firefox -> Theme" or some "Core -> Layout",
       so leaving "Firefox -> Untriaged". Probably it's connected to bug 477157

Video:
> screencast 1:   https://dl.dropboxusercontent.com/s/7kudx7439h968wx/screencast%201%20-%20white%20vertical%20lines%20are%20displayed%20within%20a%20tab.webm?dl=0
> screencast 2 (normal DPI works fine):   https://dl.dropboxusercontent.com/s/l8r9ugvofszo3bi/screencast%202%20-%20no%20vertical%20lines%20within%20a%20tab%20on%20normal%20DPI.webm?dl=0

Comment 1

[Kelsey Gilbert [:jgilbert]]

Can you attach a copy of your "about:support" page's Graphics section?

Comment 2

[arni2033]

Attachment: useless Troubleshooting Information (arni2033, comment 2).xht

Comment 3

[Bas Schouten (:bas.schouten)]

Hrm, this is slightly more likely to be layout. We're probably not rounding out somewhere correctly or something of the likes. Matt, what do you think?

Comment 4

[Matt Woodrow (:mattwoodrow)]

Yeah, that's almost certainly the issue.

I don't have time to look into this right now though unfortunately.