rem: var pref = document.createElement("preference"); pref.setAttribute("type", "bool"); pref.id = prefName; pref.setAttribute("name", prefName); document.getElementById("securityPreferences").appendChild(pref); 
add: var pref = document.getElementById(prefName);  if (!pref) { pref = document.createElement("preference"); pref.setAttribute("type", "bool"); pref.id = prefName; pref.setAttribute("name", prefName); document.getElementById("securityPreferences").appendChild(pref); } 
context:   _userAgreedToPhishingEULA: function (providerNum)  {    // create the opt-in preference element for the provider    const prefName = "browser.safebrowsing.provider." +                     providerNum +                     ".privacy.optedIn";    var pref = document.createElement("preference");    pref.setAttribute("type", "bool");    pref.id = prefName;    pref.setAttribute("name", prefName);    document.getElementById("securityPreferences").appendChild(pref);    // only show privacy policy if it hasn't already been shown or the user    // hasn't agreed to it    if (!pref.value) {      var rv = { userAgreed: false, providerNum: providerNum };      document.documentElement.openSubDialog("chrome://browser/content/preferences/phishEULA.xul",                                             "resizable", rv);      // mark this provider as having had its privacy policy accepted if it was      if (rv.userAgreed)        pref.value = true;      return rv.userAgreed;    }    // user has previously agreed    return true;  },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/10234/246b81dc9ca71cbf5ffe9bfdd64564bfe5771636/security.js/buggy/browser/components/preferences/security.js