Here is another issue I just filed last night:
https://github.com/mozilla/browserid/issues/809
tl;dr: Super minor, but the case of buttons is actually important UX too.
I'm worried about BrowserID UX because we are implementing it on our site as an additional login system along with Facebook Connect. I'd love to see BrowserID become successful since we need an alternative to Facebook and OpenID is a train wreck. But, I worry that with bad UX, it will remain just an unused interesting idea.