I think it's meant for mobile users (the domain is m.microsoft.com).

Probably it is optimized for iOS and Android.

Wait until Firefox hits the version 10.0[1]. The article has a good point too. Chrome got it right with version numbering that doesn't appear important.

[1] http://dev.opera.com/articles/view/opera-ua-string-changes/

Doesn't work under Firefox 7, Safari 5.1 or IE8 either.

It works fine for me with FF 8.0

It works in Safari if you set the User Agent to iOS (in the developer menu)