Back in the day I used Firefox's built-in Live Bookmarks for all my RSS; I still miss it, but Brief is objectively better. People always seem surprised when I tell them that RSS readers can be embedded in the browser and not just dedicated websites/apps.
A great reason to have Brief (or probably any other RSS browser plugin) instead of an app: on any site you can click on the in-browser button to subscribe to the RSS feed, which often finds feeds that aren't directly linked anywhere on the page. A lot of websites have quietly removed their feeds from public viewing but have kept them, still updating, in the file directory.