One common way to reduce the load on a web server is to use gzip or deflate compression when serving to a supporting web browser. When Firefox requests an Ogg media, it advertises that it can handle a gzipped or deflated response; the HTTP request includes the Accept-Encoding: gzip,deflate header. But despite Firefox advertising that it supports gzip/deflate, you probably don't want your web server to gzip or deflate Ogg media. If you serve an Ogg media compressed, Firefox won't be able to seek in the media, or determine its duration. Since the video/audio data in Ogg files is already compressed, gzip/deflate won't actually save you much bandwidth anyway, so you probably want to disable compression when serving Ogg files.
I have added this tip to the Mozilla Developer Center article on configuring servers for Ogg media.