Sorry for the issue. We have recreated the problem and are looking into the issue. The quickest/easiest solution for now is:
1) Edit the /components/com_jfbconnect/libraries/provider/google/widget/login.php file.
2) Around line 18, you'll see:
$buttonSize = $this->getParamValue('size');
Update that to:
$buttonSize = " " . $this->getParamValue('size');
3) Do the same for Twitter in /components/com_jfbconnect/libraries/provider/twitter/widget/login.php
LinkedIn looks to have a different problem that we haven't fully determined yet, but hopefully that gets you going for now.
Thanks, and sorry for the trouble,
Alex