legacy add-on for FF: https://addons.mozilla.org/en-us/firefox/addon/hacker-news-mark-all-read/

chrome version: https://chrome.google.com/webstore/detail/hacker-news-mark-all-read/fghfahcbhpdeeaaofcefaoodmfejieok?hl=en

Maybe chrome store foxified will return to safe the day...