rem: return aCommand == "cmd_cleanUp"; 
add: var commandNode = document.getElementById(aCommand); return commandNode && commandNode.parentNode == document.getElementById("downloadsCommands"); 
context:   supportsCommand: function (aCommand)  {    return aCommand == "cmd_cleanUp";  },
meta: 8395	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/8395/42441b54422f51e39485c902f4b02d6124193ad6/downloads.js/buggy/toolkit/mozapps/downloads/content/downloads.js