FireFox does not include stylesheets with non-*.css extensions, whereas Internet Explorer does.

This page demonstrates the problem using the link tag and a *.php extension.

phpcss2.html demonstrates the problem using @import and a *.php extension.

phpcss3.html demonstrates the problem using the link tag and a *.txt extension.

phpcss4.html demonstrates that script files are not bound to a specific extension as stylesheets are.

phpcss5.html demonstrates that *.php stylesheets can be included when the Content-Type is equal to text/css