That could very easily do it.
What you need to do is go into the Plugin Manager, set the "Select Type" filter in the top right to "user". You should see the Joomla and JFBConnect User plugins (as well as some others). The "Order" column is what you should focus on. The JFBConnect User plugin must have a higher number than the Joomla User plugin. To update, change the number in the JFBConnect User plugin to something higher than the one in the Joomla User box. Then, click this little floppy disk icon next to "Order", and the new ordering will be saved.
Hopefully that helps, but if you're still confused by something, don't hesitate to post back here!