Thomas,
Thanks for telling me the browser! I definitely see the problem in Firefox, and it's definitely odd. Haven't seen that problem before.
Can you try one thing really quickly to narrow down whether it's more on your Joomla side or on Facebook's Javascript side? Simply go into JFBConnect's Configuration area, click on the Facebook API tab, and set the language override to en_US. That will force the Like / Send buttons to be in English. If they are spaced correctly, it means it's likely a locale issue with Italian and their buttons. If so, we'll have to report it as a bug to them. If not, then it likely means there is some style in your template causing the problem. However, like you mentioned, I can't see anything that would be the problem. Once you dig down pass the fb:like tag in the styles, those are all controlled by Facebook, and can't be overridden, just so you know.
Hope that helps narrow down the issue!
Thanks,
Alex