Firefox: Force to always show menu bar

One thing that annoys me is when web-sites use pop-windows and hide the menu-bar in those pop-windows. You can tell Firefox to ignore the request to hide the menu-bar:

• Enter "about:config" in the address bar and filter for "menu".
  
• Double-click on the line that reads "dom.disable_window_open_feature.menubar", which should change the value-column from "false" to "true".