Aha!

I've no idea which version of GMail I'm on, but while searching I saw a link saying "Older version" near the top-right corner of the screen.  Clicking that, gmail reloads itself (and now displays a "newer version" link).

The older version shows the FireGPG buttons correctly.

Thanks!
-j

Hi, I'm having the same problem on 0.4.9.  I don't suppose it couldd be some setting in GPG, right?