Thanks, Bastien. It's the default value - I've not changed it:

org-file-apps is a variable defined in `org.el'.
Its value is ((auto-mode . emacs)
 ("\\.mm\\'" . default)
 ("\\.x?html?\\'" . default)
 ("\\.pdf\\'" . default))


On Mon, Feb 4, 2013 at 4:20 PM, Bastien <bzg@altern.org> wrote:

> Hi Zhenjiang,
>
> zhenjiang xu <zhenjiang.xu@gmail.com> writes:
>
> > when I type the keys `C-c C-e b', the html is generated but it is
> > opened in emacs instead of an internet browser. Does anyone know
> > why?
>
> Check the value of `org-file-apps'.
>
> C-h v org-file-apps RET
>
> Hope this helps,
>
> --
>  Bastien
>