Simo, I have just had a look to see if I could help you out, but I can't find it either. I did trade with them for several months, however, I also had an account with another broker which gave me access to WebIress - and I used that for market depth (plus a lot of other useful information not readily found with OX).
While I found them generally good for trading two legged option combos, their website does not appear to update dynamically. I had to refresh manually or set it up on an automatic periodical refresh, so found WebIress much easier.
I will have another look tomorrow when the markets are trading again to see if I can find market depth - otherwise suggest you give OX a call.