t is made in <nobr><code>startup.lisp</code></nobr>:
<pre class="pretop">
  (defvar *preferred-browser* 
      ;; On Mac OSX we defer to the OS default browser:
      #+(or macosx darwin)
      "open"
      ;; LispWorks (non-Windows) and SBCL do not search PATH for programs, so
      ;; the path must be explicitly included in the preferred browser setting:
      #+(or (and lispworks (not win32)) sbcl) "/usr/bin/firefox"
      #-(or macosx darwin (and lispworks (not win32)) sbcl) "firefox")
</pre>
</p>
<p>Sp