Oracle EPM Version where issue was found: 188.8.131.52.500
A couple of our clients have experienced an interesting issue since Firefox version 50 was released where the Menu Bar would not display any sub-menu items when selected.
One workaround found was to install the Firefox Add-On XUL Gear which solved the problem. This is in addition to the usual Remote XUL Manager Add-on needed for Oracle EPM Workspace to work with Firefox in general.
Credit to Arlene Baker for discovering the workaround.