There is a website where I can order free coupons for a local service.
The website only seems to accept * coupon order per pc.
The website seems to be able to identify a pc that has previously visited the website.

I took these steps:
- deleted all cookies in Firefox
- changed my IP address by using TOR

If I try to order again using my own pc, the order is not accepted
If I try to order again using another pc, the order is accepted

Am I overlooking something that is disclosing identifiably information about my pc?

Thanks,
Vinny