The icon is displayed only for pages that have been discussed on Hacker News.
Ctrl+Y: open comments in a new tab
Alt+Y: open comments in the current tab
The extension does not collect any data. Note however that the URLs of pages you visit will be sent over https to HNSearch (https://hn.algolia.com) which is hosted by a YC company Algolia.
The extension does not have permission to access data on websites you visit.