Firefox 2.0 has a nice RSS/Atom feed preview feature, which pretty-prints the feed and allows you easily subscribe to it in a feed reader. While this is nice from a user's standpoint, it can get in the way when trying to debug or otherwise see a raw feed as a developer. There is no option to turn this mode off, which seems to be making some people unhappy.
To help with this use-case, I made Feed Proxy, a simple service that gives you back the raw XML output (by adding a 512 byte dummy header that makes Firefox not invoke its feed preview code). Its page has more details on how to invoke it and what its caveats are.