Add this bookmark to your toolbar:

javascript:location.href='http://validator.w3.org/check?url='+document.URL;

I know it works on Mozilla 0.97, 0.98 and Netscape 4.78

E2 Writeup, Copyright 2002 Frank Grimes.

This writeup is dedicated to the public domain. Do with it what you will. (For details, see http://creativecommons.org/licenses/publicdomain/ )

--Frank Grimes, 2007