Good add-on, I like it. However, adding feed isn't an easy process. Copy-paste URL, then copy-paste title, and repeat this for every feed... is really burdensome. An option of using another way to add feeds is needed. There is a lot of ways to choose from (or may be using some of them): getting feed's URL from address bar, current page, living bookmarks, etc.
Another point is that play buttons are too small to be distinquished easily. I think making them as large as "feed" or "add feed" sign and, maybe, just square or without any frames (circles take additional space), would be preferable.