Is it possible to add a background image to all ‘layers’ of an animated gif?

In the GIMP it is possible with the multi-layers-merger extension from here:

(original)
http://registry.gimp.org/node/26135

(archived project)
https://github.com/pixlsus/registry.gimp.org_static

(location of plugin extension within that project)
https://github.com/pixlsus/registry.gimp.org_static/tree/master/registry.gimp.org/files/

Install the extension, then

1. Create a new image the same size as your animation, and put your background image in a single layer in the new image.

2. Go to Layers > Multi Layers Merger

3. Deselect all the options but “Use only active layer”. This means to only merge the active layer of the background image.

4. Make sure the “Second Image to merge with” dropdown is the image with your animation frames in it

5. Click OK, and a new image should be created with your background behind each frame.