Bugzilla

Here's a reduced testcase.  There's a red box that's indicating roughly where the submenu would be appearing.

With traditional scrollbars (that Google Docs is trying to force), that red box doesn't overlap anything and it can be hovered / moused into.

With overlay scrollbars, that red box gets covered up by the overlay scrollbar and can't be hovered/moused into.

Here's a reduced testcase.  There's a red box that's indicating roughly where the submenu would be appearing.

With traditional scrollbars (that Google Docs is trying to force), that red box doesn't overlap anything and it can be hovered / moused into.

With overlay scrollbars (e.g. Firefox & WebKit-if-you-untick-the-webkit-scrollbar-styles-here), that red box gets covered up by the overlay scrollbar and can't be hovered/moused into.