FirePHP is designed to collect log information while the PHP script executes and then sends it in special headers along with the page response. It will not show logging calls in Firebug in realtime.
To debug your code using logging, place more logging calls into the loop. e.g.
$this->firephp->log("value", $value);
You have a loop that assigns a new value to $value
on each iteration but don't use it in any of the statements in the loop. That does not seem right.
If you need realtime debugging I suggest using xDebug or other realtime logging tool.