I want to edit an animated GIF.

For the life of me, I don't understand what I might be doing wrong. When I open the file, I can see that it has 16 layers. When I chose 'animate' I see the 16 frames and every thing looks good. I am then adding an element to each layer (sunglasses). Once I edit each individual layer, I 'merge down' so that I am still seeing 16 layers. Unfortunately, although the layers all look correct, now the frames are all identical. It give the appearance of a still shot.

Can someone offer any advice?

note that in layers 9 thru 11 the baby has his arm up. This is not represented in the frames.

Not sure what you did wrong, but I might have something for you that makes the whole thing easier.
After you imported the gif and see the whole animation as separated frames, you go to the animation menu and choose Convert to Timeline



If it's ok, the whole animation still works as it should, but the funny thing is that now you can add a layer all on top of the others and put your glasses there. You'll see that in the whole animation you see these glasses.
This might solve your problm and it's easier than the way you did it (I hope)

With a fair bit of manipulation I hoped to avoid, it finally worked.

Thanks for your suggestion. I could not have done it with out using timeline it seems.

Wow, what a great tip ! Thanks, Waz.
I am looking since a long time how to easy modify an animated gif and this is a really easy way.