Tested with a blank new profile, OS X trunk nightly. Start private browsing, and the about:privatebrowsing page shown has "Learn More" shown as normal black text at the bottom of the page. It's a link, so should be blue and underlined... Indeed, as soon as I hover over it it switched to look like that, and remains that way after moving the mouse elsewhere. Possible fallout from bug 461199? The link is slightly unusual in that there's no |src| attribute in the XUL (I assume we do an onclick thing), but I'm pretty sure we do that in a number of other places in the UI. <a id="moreInfoLink" target="_blank">&privatebrowsingpage.learnMore;</a>
What is your build identifier? I just recently fixed a bug about this (bug 550661).
I just tested it on a build with the fix from bug 550661, and I couldn't see the problem.
Yep, I was one day out of date. Whee, easy fix! ;)