Have you tried just putting the main website URL into your reader? Many support autodiscovery[1], as long as the site has the proper HTML tags set up.

[1] http://www.rssboard.org/rss-autodiscovery

Firefox has a Subscribe button which you can use, though it is not there by default (to get it, open the customiser, at the bottom of the menu, and you can then drag that Subscribe button into the menu.)

View source and search for "feed" or "rss" or "atom" or even "xml".