[codedokode]

Because the site can compare the user agent with navigator.platform, which your browser fills with great care.

[userbinator]

That naturally implies we must patch the browser.

"Source code? We don't need no stinkin' source code!"

[codedokode]

That's what Russian underground hackers do to create so called "anti-detect" browsers, which can emulate different browser fingerprints. But they are commercial and closed-source.