Problem: When I add more themes to my Firefox Sync, one just goes away without notice (September 23, 2018)
I'd like the ability to sync more themes to my Firefox Sync than I can now, especially since starting with Firefox 64.0 Stable's release on December 11, 2018, I plan to contribute one picture cropped to 3,000 pixels across by 200 pixels down taken by my good friend Carol M. Highsmith to the available Firefox Themes bi-weekly of New York (especially downstate), New Jersey and Connecticut to start with.
Opaite Mbohovái (1)
As far as I know you can only have the theme your using. It sometimes does not even like that.
What your asking is to make Sync A storage device which it is not, it is to Sync 2 or more devices only. If your using it as a storage device you will loose your data.
I have no idea what your talking about re cropped pictures. There is Dropbox and you have storage with your Win10 account if using hotmail/outlook.
Moambuepyre