The page contains two buttons, from twitter and from facebook.
What I\'m observing in Firefox 3.5.15 is:
I solved this by taking Guðmundur Þór Magnússon's answer and adding margin-bottom: -2px !important; to the CSS rule:
margin-bottom: -2px !important;
.twitter-share-button[style] { vertical-align: text-bottom !important; margin-bottom: -2px !important; }