rem: hideButton(prefArray[i],prefBranch.getBoolPref(prefArray[i])); 
add: document.getElementById("button-" + prefArray[i]).hidden = !(prefBranch.getBoolPref(prefArray[i])); 
context: function ShowHideToolBarButtons(){  var prefBase = "mail.toolbars.showbutton.";  var prefBranch = prefServices.getBranch(prefBase);  var prefCount = {value:0};  var prefArray = prefBranch.getChildList("" , prefCount);  if (prefArray && (prefCount.value > 0)) {    for (var i=0;i < prefCount.value;i++) {      hideButton(prefArray[i],prefBranch.getBoolPref(prefArray[i]));    }  }}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/7cccc43f4eb240a738eadbb7ed75ac594b90d5d7/mailWindow.js/buggy/mailnews/base/resources/content/mailWindow.js