[Zope] Back button (off topic?)

Hi, I am attempting to implement a back button in my zpt page. The following code works in IE but not Mozilla Firebird. When I click the button in Firebird nothing happens. I have checked the options in Firebird and javascipt is enabled. Does anyone know what could be causing this behavior? <input type="button" value="Back" onClick="history.go(-1);return true;"> Thanks, Mike