https://www.bleepingcomputer.com/news/software/mozilla-to-remove-support-for-built-in-feed-reader-from-firefox/

Mozilla engineers are preparing to remove one of the Firefox browser's oldest features —its built-in support for RSS and Atom feeds, and inherently, the "Live Bookmarks" feature.

All Firefox users are probably well accustomed to this feature, albeit not many have ever used it.