When Hacker News links to the page you're viewing, the toolbar button will display a badge with the number of comments. Click the button to open the comments in a new tab. When the page hasn't been posted on HN, the button will open the "submit" page with url/title pre-filled.
One caveat is that the badge isn't updated in real time, only when the URL changes.
If there are multiple linking pages on Hacker News, it will pick up the one with the most comments.
The URL fragment (the part after #) is stripped when looking for the referencing HN page.
Source code: https://github.com/ivan7237d/hn-comments
Extore is a team of professionals who are passionate about creating extensions for web browsers. This devotion also gives us opportunity to appreciate work of other people. We get inspired by useful, open source extensions made by developers all over the world. Our strong belief is that one should share helpful add-ons with others. That’s why we’d like to present you our ever-growing list of favourite extensions that have inspired us. Moreover, as you probably have already learned, sometimes struggling for the best brings an end to the good. Talking about add-ons it often turns out that an upgrade is worse then previous version. Also it can become really tricky to get back to the beloved version of your favourite extension. That’s why we’re going to make not only the latest, but all versions of our favourite (and we hope yours too) add-ons available for download. No more compromises, just stick to the version you really like!