I want to toggle on/off the OSM layer to see what is in the Bing aerial image.
How to do that in the OSM online editor?
I can't find an option to disable the data layer completely. But you can select Map Data in the panel on the right (shortcut F), open Map Features and disable individual features you don't want to see.
Note: Such questions are better suited at http://help.openstreetmap.org.