We have only a few remaining instances of the "listbox" element in production code. The one in "sanitize.xul" provides checkboxes, but all other cases just look like plain lists, and the only feature that they are using that is specific to "listbox" is the "rows" attribute to set the element height. We can easily convert these to use "richlistbox", and we can just set a height on the element that isn't a multiple of the row height, like most lists in the user interface already do. This allows us to remove several listbox-related bindings, as well as hundreds of lines of layout code that only supports features like the "rows" attribute.