The option menus already use OpenGL scissoring to cut off the last element, so rendering a border around all elements should be trivial. This should help separating popups better from the browser content, especially with similar background colors.
To make sure the border looks sensible, it would be nice to give the opener some control over where borders should be displayed. The history popup likely only wants a border on the top for example, while the input drop-down likely wants borders everywhere (with the top one being potentially optional).
The option menus already use OpenGL scissoring to cut off the last element, so rendering a border around all elements should be trivial. This should help separating popups better from the browser content, especially with similar background colors.
To make sure the border looks sensible, it would be nice to give the opener some control over where borders should be displayed. The history popup likely only wants a border on the top for example, while the input drop-down likely wants borders everywhere (with the top one being potentially optional).