Themes for Sitecore collects no data and sends nothing to its developer or to any third party.

It stores, in the browser's own extension storage only (which the browser's sync, if the user has it on, may copy to their other devices): the theme chosen for each Sitecore host, each host's detected Sitecore version, per-site display settings (title postfix, tab icon tint, environment), and any themes the user imports.

It only contacts the Sitecore hosts the user enables from the toolbar popup, and the theme URLs the user imports.

Full policy: https://codality.net/themes-for-sitecore/privacy/