The Animated GIF Restore setting sets what happens between each frame in an animated GIF:

Nothing means no action is taken. Many browsers take this as meaning the same as the Leave As Is option.

Leave As Is displays the frames one on top of another - this leaves many frames visible in a stack if some are transparent. Some browsers clear the animation before it loops again, some do not.

Background restores the area covered by the graphic to the background color of the GIF (usually white).

Restore Previous restores the area covered by the frame to what it was before the frame was displayed. This is interpreted by some browsers to mean that the frame should be cleared to the background before each frame is displayed and by others to mean that the frame should be shown on top of the previous frame.

As browsers interpret these values in different ways, you may need to experiment to achieve the desired result.