TLDR This doesn't store any user data. The only thing collected from the user is the URL of the article that they want to get summarized.
For example, if a user clicks on the addon when on a particular webpage, the addon will send the link of the webpage to an endpoint on https://tldrthis.com where the content of the webpage is scraped, summarized and then returned back to the user.
Neither the link of the webpage nor its content nor its summary is stored on https://tldrthis.com or anywhere else.