Select More info on a study in test pilot, then select a link - most of the links that are meant to open a page open in the compose window.
I think for now, we can either open them in a content tab or in the external browser.
This doesn't happen for me, though the links do open in the little study window, which is probably wrong. I'm thinking opening them in an external browser is the right thing to do, since the links point to things like the Google Group, and we should just take advantage of the fact that the user is probably logged into Google in their browser (but not in Thunderbird's content tabs).
This got fixed in bug 709737.