See the readme:
“This plugin causes TiddlyWiki to continuously save the contents of
each tiddler that is changed as a JSON file. Configured correctly, the
browser will download the files silently in the background, and they
can be used as a backup in case of accidental data loss.”
Inspired by @telmiger’s comment (3) here:
https://github.com/Jermolene/TiddlyWiki5/issues/2741#issuecomment-276128
871