This addon extracts from mudcat pages:
1 The thread number of posts viewed, and the latest post number in each. This is to identify new posts and scroll to them.
2 The text of the latest post. This is so that the text can be recovered with the 'Recover text' button.
3 The poster of the latest post if not signed in. This is used to pre-fill the name next time. It does not extract the name of signed-in users.

The addon needs to store this data in order to work.

The data is stored within the browser's local storage. No data is sent anywhere or shared with any other system.

The optional post archiving feature send posts to a companion program running on the same computer which writes them to text files in the local filesystem or a network drive. No data in addition to the text of the publicly-readable posts is sent.

The user must specifically grant permission to "Exchange messages with programs other than Firefox" to use this feature.