[Project_owners] Firefox/SeaMonkey API parity

[Neil]

As part of bug 240393, Justin Wood suggests that we should try to keep 
parity with the Firefox API, in particular:

isValidFeed(aData, aPrincipal, aKnown) - unless aKnown is true, verifies 
aData against a feed-detection algorithm; always performs a security check

contentPrincipal - property on tabbrowser, shorthand for 
contentDocument.nodePrincipal

FeedHandler.subscribeToFeed(aHref, aEvent) - subscribes to the feed 
defined by the href or event

Does anyone actually use these?