It'd be fun to say "Changing your RSS font type is as easy as pie"—but have you ever tried baking a pie? It's not the easiest thing in the world. But changing your RSS font type…is!
Open a feed by clicking it in your "All RSS Feeds" pull-down menu. Do you see the font pull-down menu at the top of the window? It might be a blank rectangular white box if you haven't changed fonts yet—when you change fonts, your choice is displayed in the box. Scroll down and pick a font, any font.
Your choice updates all feeds, not just the one you're looking at. And we'll remember it the next time you log in!