code: public void doIconSize( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
          String qs = req.getQueryString();
          if(qs==null)
              throw new ServletException();
          Cookie cookie = new Cookie("iconSize", Functions.validateIconSize(qs));
          cookie.setMaxAge(/* ~4 mo. */9999999); // #762
          rsp.addCookie(cookie);
          String ref = req.getHeader("Referer");
          if(ref==null)   ref=".";
          rsp.sendRedirect2(ref);
      }
docs: Changes the icon size by changing the cookie