http://jntlesnev5o7zysa.onion seems to be the official one, according to https://twitter.com/tpbdotorg/status/203221129513545729

Yes, but:

1. That tweet is from May 2012.

2. The other URL is in the address bar in the screenshot on the Pirate Browser web site. The screen shot has a time stamp of August 2013.

So the first URL was probably the official one in 2012, but it has possibly been superseded by the other one.

Saying this just made something snap into place for me. Right now, we have things like Adobe Air and node-webkit, that basically just ship an address-bar-less browser, which can be used to make a webapp look like a real app (e.g. Light Table.) And we have Tor. But no one, as yet, has thought to combine the two--for example, by making an app that has an automatic-updating mechanism that updates from an .onion source, so nobody knows who the developer is.

I think I might work on this, if anyone is interested in using the result.

I'm a lot more inclined to seek out more information about the authors of the code I execute than I am to start using code that comes from exceedingly difficult to trace authors.

(So right now I am lazy about it but really only see things going in one direction, towards being more careful about knowing)