add:  if (!viewPicker) return;  
context: function ViewChangeByValue(aValue){  var viewPicker = document.getElementById('viewPicker');  if (aValue == -1)  {    viewPicker.selectedItem = null;    viewChange(viewPicker, -1);  }  else  {    viewPicker.selectedItem = viewPicker.getElementsByAttribute("value", aValue)[0];    viewChange(viewPicker, viewPicker.value);  }}
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/a7fd2a241c2b0fee42ba464c936e542088f5559b/msgViewPickerOverlay.js/clean/mailnews/extensions/mailviews/resources/content/msgViewPickerOverlay.js