Browser identification

[Wickham]

When I use Stefan's tutorial to identify browsers using PHP

 

<?php $_SESSION['browser'] = $_SERVER['HTTP_USER_AGENT']; ?>

 

I get this using IE7:-

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)

 

and this using Firefox:-

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5

 

What is the Mozilla/4.0 reference in the IE7 output and what are the Windows references in the Firefox output? General explanation please.

[shelfimage]

IE did this to accept content from Netscape browsers so long long ago and kept it:

from wikipedia:

 

The earliest example of this is Internet Explorer's use of a User-Agent string beginning "Mozilla/ (compatible; MSIE ...", in order to receive content intended for Netscape Navigator, its main rival at the time of its development. This was not a reference to the open-source Mozilla browser, which was developed much later, but to the original codename for Navigator, which was also the name of the Netscape company mascot. This format of User-Agent string has since been copied by other user agents, partly because Explorer, in turn, came to dominate.