garbear/facebook-mediawiki — comment on commit 48d16dd5a68b0bee9828ed8690ce04a15d1c9ed3
File:  line 0
By garbear:

From the MediaWiki extension page:

"You may notice that your Facebook extension is still not functional. When going to special pages -> Log in with Facebook, you get a database error, where you can observe that you have a duplicated database prefix. To fix this, find the offending line and change it as above. This should eliminate your double prefix issue."