AutoHighlight doesn't collect any data.
User preferences (options page data) are stored only locally and are accessible only by extension itself.
User defined highlighting rules are stored in the "browser.sync" storage which browser can synchronize across devices.
This feature is NOT supported in Safari.
To make it work in other browsers, you need to be logged in your browser specific profile and addons data synchronization must be enabled.
Firefox is using end-to-end encrypted Firefox Sync engine.
- "Access your data for all websites" - is required for every addon that needs to modify any page without user interaction (without clicking the toolbar icon or using the context menu item)