All map controls such as zoom in/out (plus/minus) and later - editing controls should be fixed relative to the map viewport, not the map container.

For example, when editing the map at vem3.wmflabs.org home page, in the editor dialog the map is bigger than the viewport. The map has a number of controls (at this point - only two - the zoom in and zoom out [+][-] buttons). If I scroll the map (using the scrollbars or mousewheel), the zoom controls would move out of the view. If we enable editing buttons, they will be more important to always stay visible.