I get the error on a fresh install.
The bug is simple to fix :
in the file /FirePhp/lib/Insight/Helper.php
in the function init()
replace the line : if($clientInfo = self::$instance->getClientInfo()) {
by the following : if($clientInfo = self::$instance->getClientInfo() && isset($clientInfo['authkeys'])) {
Keep up the good work.
Cheers from France ;-)