まあこんな感じで
document.getElementById('context-savelink').addEventListener('click', function(aEvent) {
if (aEvent.button == 1) {
urlSecurityCheck(gContextMenu.linkURL, gContextMenu.docURL);
saveURL(gContextMenu.linkURL, gContextMenu.linkText(), null, true, true, makeURI(gContextMenu.docURL, gContextMenu.target.ownerDocument.characterSet));
closeMenus(aEvent.target);
}
}, false);