Looking at the requests made to Google, it seems like you have an SEF extension that's altering the URLs they are using. At first, Google is requesting the proper URL that looks like below (the long strings will be different for each authentication):
index.php?option=com_jfbconnect&task=authenticate.callback&provider=google&state=b0c43602cfad9ddacbcdcbfb2d1262be&code=4/yAEyP_lOAd3f96hYFjo1t7kDmPAle2O0pEObvHXOv2H2N3b0yD4Br4HByTRF8aw0GtGJQ4kz1wFGbE_QpTG6DGo
But then, something on your site is performing a 301 redirect to:
/component/com_jfbconnect/authuser,3/code,4/yAEyP_lOAd3f96hYFjo1t7kDmPAle2O0pEObvHXOv2H2N3b0yD4Br4HByTRF8aw0GtGJQ4kz1wFGbE_QpTG6DGo/hd
That doesn't look correct.
Can you disable SEF URLs (temporarily) to see if that fixes the issue? If so, then please investigate how to have whatever SEF extension you're using 'skip' generating pretty URLs for JFBConnect. They shouldn't be necessary.
I hope that helps, but if you continue to have issues, just let us know.
Thanks,
Alex