Unecessary Flashing of Menubar Dropdown

[handshaper (Robin Mair)]

We had this problem some time ago, but it seems to have resurfaced. When previewing a page in the browser the dropdown menu in the menubar is drawn on the screen. This also happens sometimes when the page is refreshed, not all the time. See the GIF below.

Interestingly, it seems to also be expanding the sub-menu within the dropdown, which is why the dropdown is so long.

[ben]

This is happening due to the component not being hidden before the JavaScript for the page has loaded — but this one is pretty easily fixable, so I’ll add it to me list