I have not worked on Firefox4 (but on 3.6 ) , but did you forget to enable the console / scripts ?
有没有人使用firephp与firefox 4和Zend Framework DB Profiler？
I can't see the log in the console. The headers show the log, but nothing show up on the console. I've tested the Zend_Log_Writer_Firebug and everything works fine.