1327639 - Tabs twitch during drag and after drop when I drag-n-drop them

Status: NEW

(Firefox :: Tabbed Browser, defect)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 49, 32bit, ID 20160526082509
STR (for screen 1366x768):
0. Set DPI -> 100% :
 A) Set DPI level -> 100% in your OS   [OR]
 B) Set layout.css.devPixelsPerPx -> 1.0
1. Open new Firefox window, open 8 tabs in that window, enable title bar.
2. Hover mouse over penultimate tab, hold left mouse button to start drag-n-drop
3. Move mouse over "New tab" button. Wait 3 seconds
4. Release left mouse button

AR:  In Step 3 right side of last 2 tabs twitch by ~1px. In Step 4 the last 2 tabs twitch by ~1px.
ER:  Tabs shouldn't twitch.

Note:
 This doesn't only happens with title bar enabled, and not only on screen with resolution 1366x768
 STR contains Step 0 to prevent confusion, because there's already a lot of extra twitching on HiDPI