在Firefox中更新用户代理

Question

I would like to change my User Agent while browsing and display the changes on a website. I already got a website that prints the UserAgent, simply using JS document.writeln(navigator.userAgent) .

When I load this page with Chrome, it displays my default UA (let's say abc ). When I change it to xyz and refresh (Ctrl+F5), it displays the new UA xyz . Great, that is exactly what I wanted!

Now if I do the same thing with Firefox, the displayed UA won't update. So I load the page with abc as my UA, I change it to xyz , refresh the site (again without cache) but it still displays abc .

The Apache logs and Wireshark both show that the UA transported in the HTTP header is actually the new xyz .

Does anyone of you have an idea what is happening here?

Answer 1

This is by design. From MDN :

In Firefox, you can change the preference general.useragent.override in about:config. Some Firefox extensions do that; however, this only changes the HTTP header that gets sent, and doesn't affect browser detection performed by JavaScript code.

Answer 2

As some of you suggested I had read the navigator object, not the actual HTTP header, thanks for that!

I solved it using PHP instead:

    <?php
        $header=getallheaders();
        foreach ($header as $name => $value) 
        {
            echo "$name: $value<br/>";
        }
    ?>

Or just

    <?php
        $header=getallheaders();
        $ua=$header["User-Agent"];
        echo "$ua<br/>";
    ?>