So, if I install the Artist Slideshow on one device, does it duplicate across devices?
In general, addons are required (at least official ones) to store all their data within the profile folder in which they run (though they might support remote storage for example at a web site).
scott s.
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If the addons use the library you're sharing, yes. For example the YouTube addon uses the video library, so the watch status of YT videos is shared. But the applications settings itself are not shared.