Animated GIF Export Dialog Box - Animation Restore

This sets what happens after each frame has been displayed. Nothing means no action is taken, though many Internet browsers take this as meaning the same as the Background option. Leave As Is displays the frames one on top of another - this leaves many frames visible in a stack if some are transparent. Background restores the area covered by the graphic to the background color of the GIF (except where the frame is transparent). Restore Previous restores the area covered by the frame to what it was before the frame was displayed.

Note that the way browsers interpret these values can vary, you may need to experiment to achieve the desired result.