This might be related to Bug 49524.
See https://commons.wikimedia.org/wiki/File:VE_selection_box_goes_over_menus.png
When you open https://en.wikipedia.org/w/index.php?oldid=620028233 in Firefox on Windows 7, the sandbox template is autoselected. If you click on a menu (e.g., to set bold text), the menu drops down but the items that overlap with the auto-selected template can't be chosen.
I am unable to reproduce this in either Safari or Firefox on a Mac.
Version: unspecified
Severity: normal