I found a very strange behavior of FF and firebug too. If u have started firebug and running GD then it will give that error and if u close or stop using firebug on FF then Maps will start working fine.
Hi,
I really apologize for this inconvenience. It will be fixed in next release.
Meantime plz download attached zip and extract .php file from it and upload it to ur core geodirectory > geodirectory_functions folder.