This installer will evaluate a RSS data source, and if it is valid give you a preview and allow you to install that source as a Mozilla Sidebar.
Or, rather than type a URL in above, you can choose from a number of my favorite RSS sources.
Tips on finding RSS Sources: There are a number of resources to find the URL of the RSS sources you are looking for. The above list is short and highly subjective (i.e. what I am interested in). If you are looking for a RSS feed of a different nature, try XMLTree and my.userland.com (Userland requires you to register). The more people who add a particular feed, the more likely I will add a direct link to the feed.
The author, Corvar, welcomes comments.
This script owes quite a bit to the work of DJ Adams on his mysidebar.pl script.