When using the Download Manager extension, the image url for #dmStartButton must point to 'chrome://browser/skin/Toolbar-small.png' (the location of this image in the default "classic" theme) or the image will not display when 'disabled' - the entry for #dmStartButton[disabled="true"] in mozapps/downloads/downloads.css is ignored.  Need to de-bug in future.

The file Toolbar-small.png is used for no other purpose than to display #dmStartButton for the Download Manager extension support.
