header("Content-type: text/css"); is working in Firefox and Chrome, but in Internet Explorer 9 it shows up as 'text/html'

Question

header("Content-type: text/css"); works in Firefox, Chrome and other, but not in Internet Explorer 9. I am not sure what's up.

In Chrome and Firework it shows the style sheet if I open it in its own tab and it's being applied to the page.

In Chrome under Network in the developer tools it says the type is text/css and the status is 200.

In Internet Explorer 9, it wants to download the style sheet if I open it in its own tab and it's not being applied to the page.

In the F12 developer tools you can click on network, start capturing and refresh the page. It shows the Style.css.php. The type is text/html and the result is 406.

This is in the head:

<link rel="stylesheet" type="text/css" href="/assets/css/style.css.php" media="screen" />

Request headers:

Key Value
Request GET /assets/css/main.css HTTP/1.1
Accept  text/css
Referer http://10.0.1.5/
Accept-Language en-US
User-Agent  Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Accept-Encoding gzip, deflate
Host    10.0.1.5
Connection  Keep-Alive
Cookie  PHPSESSID=*Hidden*

Response headers:

Key Value
Response    HTTP/1.1 406 Not Acceptable
Date    Fri, 01 Apr 2011 10:12:42 GMT
Server  Apache/2.2.14 (Ubuntu)
Alternates  {"main.css.php" 1 {type application/x-httpd-php}}
Vary    negotiate
TCN list
Keep-Alive  timeout=15, max=100
Connection  Keep-Alive
Content-Type    text/html; charset=iso-8859-1

Answer 1

IE has "No, I'm not kidding about Content-Type" switch:

X-Content-Type-Options: nosniff

BTW: make sure you also send Last-Modified and disable session.cache_limiter in PHP, otherwise browsers will keep reloading the CSS file, which will negatively impact performance.