===Chrome Elements===
[talk about Fennec tries to not use any dialogs. There are still some, used by the stack platform, but we are working to removing them all. Instead of dialogs, Fennec uses other UI to interact with the user. Firefox does similar things with modeless notification boxes and the toolbars]error pages in content.
[talk about In those situations where a dialog or secondary window would be used, Fennec typically brings a pseudo-panel into view. Fennec does not use real <code><panel></code> elements, as those tend to cause performance issues. Instead, a <code><vbox></code> containing the use of desired UI is brought into view. The boxes instead are children of panels]the <code><stack></code>, can be positioned as needed, and are hidden until needed - also to improve startup performance. Some examples are Bookmark List, Bookmark Editor and the Tools Panel (Add-ons, Preferences and Downloads). These elements are very similar to the toolstrips, but they are not managed by the WidgetStack.
==Performance Related Coding Guidelines==
