1404900 - Photon menus show scrollbar for a few ms when switching between submenus

Status: RESOLVED DUPLICATE of bug 940733

(Firefox :: Menus, defect)

Description

[TMart]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20171001220301

Steps to reproduce:

-Open a Photon menu with many items like the Library.
-Access a submenu like Bookmarks. 
-Then switch back to the Library main view


Actual results:

During transition from one (sub)menu to the other, the grey Firefox scrollbar is shown for a few milliseconds. That makes the transition look very janky and uneven. 


Expected results:

Scrollbars shouldn't be displayed at all when all items fit on the screen. 

Tried recording with a GIF recorder, but it flickers so fast that it's barely noticeable there. However on the real screen the flickering is very distracting with Photon's otherwise smooth animations.