Problem with firefox running on fluxbox/debian

Okay so I want to get firefox to run through fluxbox via VNC, however firefox wont start through fluxbox, nor through terminal, when I try and start it in terminal it says
(firefox-bin:7020): Gtk-WARNING **: cannot open display:
could anyone help me please? Thanks in advance!

check the permissions given on firefox!

is fluxbox running under the same user, you start firefox with?

is there any more output than:
(firefox-bin:7020): Gtk-WARNING **: cannot open display:

??

grz