Note that the order is: paste, click + button, then add nick (or Enter to leave blank). When the nick box disappears, it's saved. Use the drop-down button to select another of the saved URLs, you should see them all listed - and yes, only one can be active at a time.
If you want to edit the config file, the format with nick is:
Favorites=TvNZB!#!http://www.tvnzb.com/tvnzb_new.rss|Newzleech!*!http://www.newzleech.com/rss.php? n=80&g=alt.binaries.multimedia
Without nick:
Favorites=http://www.tvnzb.com/tvnzb_new.rss|http://www.newzleech.com/rss.php? n=80&g=alt.binaries.multimedia
-Hecls