The web browser will send info about itself in the User-Agent line. A browser might send you something like:

GET / HTTP/1.0
Connection: Keep-Alive
User-Agent: Mozilla/4.72 [en] (X11; U; Linux 2.2.16 i686)
Host: localhost:1101
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png
+, */*
Accept-Encoding: gzip
Accept-Language: en
Accept-Charset: iso-8859-1,*,utf-8
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