Install NewsFire on OS X and import hundreds of feeds that you no longer care to read? Frustrated by the lack of multiple-select support in the feed list (but not complaining because NewsFire is otherwise bad ass, and free)? Too lazy to press [Command+Delete]+Enter until the list is empty?
The file that you’re looking for is located at /Users/[USER]/Library/Preferences/org.xlife.NewsFire.plist, and is best edited with PropertListEditor.app.
If you want a complete purge, delete the Feeds array, and create a new one in its place.
This tip brought to you by fs_usage -ew | agrep -i 'newsfire;open'.