FirePHP is not intended to be used on production sites. The logging is only sent to the web browser. If this is left live, it can expose information that end users should not see.
What you can do is to create a class that subclasses FirePHP. Write the messages for FirePHP to the log file and then send them on to FirePHP. Give your logging class the ability to have FirePHP enabled or disabled. On deployment, disable FirePHP and have the messages only go to the log file.