I have a reasonably complex ContentPanel with about 50 widgets on it.

When the panel is opened via dialog box then there is no problem. Firefox renders the widgets off-screen and then shows the whole dialog box at once. Its fast.

However, when I dynamically create TabItem and add this panel to it then Firefox renders everything on the screen. This shows down opening the TabItem and does not look good.

Other browsers (IE, Chrome, Opera, Safari) don't do it.

Here is the slow-motion capture of what happening.

Is it possible to do anything in code to force Firefox to render the content off-screen like other browsers?