When you open an animated GIF file in Photoshop Elements 9 Editor, only the first frame of animation appears.
Download the updated GIF plug-in: GifEL.8BI. (Right-click this link and choose to save the file to your Desktop.)
All other versions of Photoshop Elements on Windows have the correct GIF plug-in to support opening animated GIF files as layers. No version of Photoshop Elements on Mac OS can open animated GIF files as layers. Photoshop CS5 is the first version of the parent product that has had this capability added.
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