rem: pref.addObserver(this.domain, this); 
add: var pbi = pref.QueryInterface(Components.interfaces.nsIPrefBranchInternal); if (pbi) pbi.addObserver(this.domain, this, false); 
context: function nsButtonPrefListener(){  try {    pref.addObserver(this.domain, this);  } catch(ex) {    dump("Failed to observe prefs: " + ex + "\n");  }}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/8403e03f3bdc8feaf5cc5f31884e180a04c93a26/fastnav.js/buggy/xpfe/browser/resources/content/fastnav.js