this should do it:
http://en.wikipedia.org/wiki/Mozilla
When users visit a website (via a user agent such as a web browser), a
text string is generally sent to identify the user agent to the web
server. It is known as the “user agent string”. The Netscape web
browser identified itself as “Mozilla/” followed by some
information about the operating system it was running on.Because the Netscape browser initially implemented many features not
available in other browsers and quickly came to dominate the market, a
number of web sites were designed to work, or work fully, only when
they detected an appropriate version of Mozilla in the user agent
string. Thus, competing browsers began to emulate (“cloak” or “spoof”)
this string in order to also work with those sites. 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, its main rival at the time
of its development. This format of user agent string has since been
copied by other user agents, and persisted even after Internet
Explorer came to dominate the browser market.
wiki knows everything
also https://superuser.com/questions/113020/why-does-internet-explorer-calls-itself-mozilla