In v3.2.2 for J1.5, I find we cannot change the text of logout button by editing en-GB.com_jfbconnect.ini or en-GB.mod_jfbclogin.ini.
I find a quick hack for it. Alex please help check if there's another quick method to change it.
In components/com_jfbconnect/libraries/facebook.php line 310, replace
$logoutStr = JText::_('LOGOUT');
with following
$lang = JFactory::getLanguage();
$lang->load('com_jfbconnect');
$logoutStr = JText::_('COM_JFBCONNECT_LOGOUT');