Most readers will also do this auto-discovery for you. So typically you can just paste the page or article URL and it will find the feed.
Of course the extension is nicer because you don't need to guess and check, you get a quick indicator if there is a feed or not.
Personally I use Want My RSS because I like the preview which then lets me know if it is a full-text feed or just summaries. This is also Firefox only. But extensions for other browsers are available.