I use Ping.fm to cross-post my updates between Twitter, Plurk, Facebook, and Status.net. Unfortunately, Mozilla F1, the latest experiment from Mozilla Labs which focus on sharing URLs, is not support Ping.fm (yet.)
So how if I really wanna use Mozilla F1 to share URL across services? Simple, just link F1 to your Gmail or Y!Mail account, and send message to your Ping.fm posting email address, that's it! It might not that straightforward, but kinda of a lifesaver workaround. You might also want to add the Ping.fm address to Contact in Gmail first, in order to auto-complete the address in the To field.
Remember to put your additional message in the mail body, since Ping.fm will ignore your message subject.