A few tips on how to avoid screen flicker during page load when working with HoverMenu and CollapsiblePanel
I use HoverMenuExtender to display a Panel related to an ASPX control. The panel contains a table containing a context menu.
Set the Panel invisible by assigning a CSS classname which sets display to none.
Set the Table to a CSS classname which defines a background.
The HoverMenu behavior will magically set display to block, thus displaying panel and table once moving the mouse over the sensitive controls.
To avoid flickers when using CollapsiblePanel, set the panel’s style to
(inline or via CSS) and, if you use images to collapse and extend, make sure the Image control is assigned a default image with the same size to avoid resizing.
Both tips make the dynamic panels visible at first, and only display them when selected.