Because of general incompetence and lack of testing, several sites fail to ensure they compress (either gzip or deflate) the content they send for some browsers but not others; sometimes sites deliberately target browsers for such treatment. This online test checks using a variety of different user-agent strings whether compression browser discrimination occurs. It will follow HTTP redirects, but not meta redirects so that is something to be aware of. Opera users can use this button to easily test a site (drag it up to a toolbar of your choice): GZip-Test
Opera 9.0 : Opera/9.00 (Windows NT 5.1; U; en)
HTTP/1.1 200 OK Date: Fri, 03 Sep 2010 18:22:00 GMT Server: Apache Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Content-Encoding: gzip Vary: Accept-Encoding Set-Cookie: PHPSESSID=5d03428ffcc3e3470cdc8cb3ea7a750f; path=/ Set-Cookie: PHPSESSID=3b1c92889f91ea5e9fff09cb075c6156; path=/ Set-Cookie: PHPSESSID=00e93d437f7bb5d440fe00755b86ceaa; path=/ Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1
cURL Time: 0.624284
Opera 9.0 (ID: MSIE 6.0) : Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; en) Opera 9.00
HTTP/1.1 200 OK Date: Fri, 03 Sep 2010 18:22:00 GMT Server: Apache Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Content-Encoding: gzip Vary: Accept-Encoding Set-Cookie: PHPSESSID=48cc7342467a991f064fafbb820887b4; path=/ Set-Cookie: PHPSESSID=f15be924bafccffb95668b20edd1012f; path=/ Set-Cookie: PHPSESSID=c3e164a923bb660331d028502579bfd6; path=/ Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1
cURL Time: 0.403272
MSIE 6.0 : Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
HTTP/1.1 200 OK Date: Fri, 03 Sep 2010 18:22:01 GMT Server: Apache Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Content-Encoding: gzip Vary: Accept-Encoding Set-Cookie: PHPSESSID=0a459d92d3c3a6ea826074de3c2f05ae; path=/ Set-Cookie: PHPSESSID=638c3e77f5b73eb8cc308e31eb6eec28; path=/ Set-Cookie: PHPSESSID=027b342f708f126809e135aa057dcc1c; path=/ Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1
cURL Time: 0.394826
Firefox 1.0 : Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511 Firefox/1.0
HTTP/1.1 200 OK Date: Fri, 03 Sep 2010 18:22:01 GMT Server: Apache Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Content-Encoding: gzip Vary: Accept-Encoding Set-Cookie: PHPSESSID=320abf48c3cfa5fb5fd7ac0234dc993b; path=/ Set-Cookie: PHPSESSID=eb48a8bd7488484975c1791a462f87cc; path=/ Set-Cookie: PHPSESSID=848713a6686236867753244ac9d0089c; path=/ Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1
cURL Time: 0.396651
Safari v125 : Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/124 (KHTML, like Gecko) Safari/125
HTTP/1.1 200 OK Date: Fri, 03 Sep 2010 18:22:02 GMT Server: Apache Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Content-Encoding: gzip Vary: Accept-Encoding Set-Cookie: PHPSESSID=a9224310540f5fb665a6469902760d9a; path=/ Set-Cookie: PHPSESSID=735e22d181a2ec7143b258d01e1a8992; path=/ Set-Cookie: PHPSESSID=c4283a8b113411867eef0c836e7db86a; path=/ Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1
cURL Time: 0.398717