rem: var url = aDocumentURI.QueryInterface(Components.interfaces.nsIURL); if (url.fileName != "") return url.fileName; 
add: try { var url = aDocumentURI.QueryInterface(Components.interfaces.nsIURL); if (url.fileName != "") return url.fileName; } catch (e) {   } 
context: function getDefaultFileName(aDefaultFileName, aNameFromHeaders, aDocumentURI, aDocument){  if (aNameFromHeaders)    return validateFileName(aNameFromHeaders);  // 1) Use the name suggested by the HTTP headers  var url = aDocumentURI.QueryInterface(Components.interfaces.nsIURL);  if (url.fileName != "")    return url.fileName;                        // 2) Use the actual file name, if present    if (aDocument && aDocument.title != "")     return validateFileName(aDocument.title)    // 3) Use the document title  if (aDefaultFileName)    return validateFileName(aDefaultFileName);  // 4) Use the caller-provided name, if any  return aDocumentURI.host;                     // 5) Use the host.}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/a824fe329f2d205d0091f5c348538eec569fe476/contentAreaUtils.js/buggy/xpfe/communicator/resources/content/contentAreaUtils.js