rem: if (printProgress) { try { printProgress.unregisterListener(progressListener); printProgress = null; }  catch( exception ) {} 
add: if (!printProgress) return; try { printProgress.unregisterListener(progressListener); printProgress = null; 
context: function onUnload() {  if (printProgress)  {   try    {     printProgress.unregisterListener(progressListener);     printProgress = null;   }       catch( exception ) {}  }}
meta: 5459	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5459/7017f5750d9b84c4e97e58393dba259da2a59e18/printPreviewProgress.js/clean/toolkit/components/printing/content/printPreviewProgress.js