UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:64.0) Gecko/20100101 Firefox/64.0

Steps to reproduce the problem:
1. Disabled all plugins
2. Cleared cached an cookies twicw0
3. Opened site in Firfox - not occurring there.

What is the expected behavior?
Menu should not be collapsed and the expand button should expand the menu but does not.

What went wrong?
Happen in mid stream scroll across screen.

Did this work before? N/A 

Chrome version: <Copy from: 'about:version'>  Channel: n/a
OS Version: 
Flash Version: Shockwave Flash 32.0 r0