then it's not the PHP
php is server side, meaning if it worked in IE and Safari, then the code put out by PHP will be the same in firefox
view source and make sure everything is nice and clean in the code that is being spit out. Firefox's brilliance and source of fustration is that it is a very anal browser, it does very little to fix or compensate for broken html code, so while IE can see something that might have been wrong, firefox wont