Our goal for including a news feed (RSS/ATOM) in the live bookmark is to demonstrate dynamic, changing and relevant content. We would suggest you choose something your users are interested in and that is locally relevant. The guidelines for making recommendations are on <https://wiki.mozilla.org/L10n:Firefox/Productization>. By default this is the same as en-US, which is BBC news. Erdenebat, do you have any suggestions? The implementation is done via a change of the redirect on mozilla.com, and is a server-side change only. The Mongolian team will be driving this bug to completion.
By opinion of Erdenebat, the default is okay. There is no good rss feed for mongolian news yet.