GMail Background GIF by Thibault Bruyère

To use a GIF as a background of GMail:

• Install this extension
• Give the extension the two permissions that it needs
  • Go to about:addons
  • Click this extension
  • Go to "Permissions" and click the two toggles
• Create a Google Photos album or use an existing album and upload your GIF in it
• In GMail you can now select your GIF as a theme (see Set a photo as your background)

Feel free to open issues and create pull requests on the github repository of this extension.

To install this extension on Chrome, follow the instructions on the github repository.