Is there any mobile browser support? I haven't tested it on any other browser except for Chrome for Android and the User list appears correctly, but the message box to a user gets stuck in the corner.

Is there a fix for this or a way to de-activate it from running on mobile browsers?

Either you can wait for the mobile support to be added , or you can add a simple check to detect a mobile browser and exit freichat script (freichat/client/main.php)

A simple mobile detection would be

if(strstr(strtolower($_SERVER['HTTP_USER_AGENT']), 'mobile') || strstr(strtolower($_SERVER['HTTP_USER_AGENT']), 'android')) {
   //You are running a mobile webbrowser
   exit;
}