Firefox \ Iceweasel Differences?
One of the most common operations performed in a Web page is to detect the browser type and version. Browser detection is performed to ensure that the content presented to the browser is compatible and renders correctly....
The quote is 100% bullshit of course. The whole idea of html was to provide the content with markup and allow the USER to customize the look in the browser. Personally I never wasted time doing anything more than selecting font sizes... Then came 'stylesheets' to encourage browsers to display something more like what the content creator wants, and here's one point where things start to break very badly. User agent detection is a Microsoftism; for the most part I get the impression that MS uses this to redirect users who don't use IE* to some crap site to give the impression that the browser is broken (see stories on MS campaign against Opera).
As for complex sites and things that work/don't work - making use of server-side scripts should ensure that everything works as long as it is content supported by the W3C standards and the version of the standard coded into the browser. For those site designers who require the use of proprietary codecs like 'Flash' just to view and browse a website, we have a special name: moron. Standards good, proprietary crap bad. Proprietary crap claiming to be standard: must be Microsoft.