A ZIP with:
* A GIF exported from your XCF
* A checkerboard pattern background
* A HTML file to play the first over the second in your browser
https://www.dropbox.com/s/x87m65kf08sgl9...l.zip?dl=0
The whole thing works. So the next step is to try with the GIF you exported.
Btw, you have an extra black background frame that you may want to remove, and you should really be using "replace" mode.
* A GIF exported from your XCF
* A checkerboard pattern background
* A HTML file to play the first over the second in your browser
https://www.dropbox.com/s/x87m65kf08sgl9...l.zip?dl=0
The whole thing works. So the next step is to try with the GIF you exported.
Btw, you have an extra black background frame that you may want to remove, and you should really be using "replace" mode.