Hi there, it’s most likely because back button does not trigger window.unload event in Firefox and Safari which is used to hide the preloader.
More info here: http://bugs.jquery.com/ticket/8684
If you wish a page reload just bind an event to to window.unload
jQuery(window).unload(function(){});
in /js/scripts.js
It can be at line 6, after the window.load event handler
Thanks