2014 on the Internet means that things have to work cross-browser/cross-platform. We can never be sure what browser a client is using, that's why I always check my blog and website on different browsers, and on a Mac and tablet, when I can get my hands on them.
If, for instance, I tried to use a coupon on DickBlick.com (or wherever), and was told it would only work if I installed a different browser or version . . . I'd probably skip it, and find a good deal elsewhere.
There are too many shopping options to expect potential buyers to jump through hoops.
Thanks for the update, Iris. Just yesterday, I offered someone a discount code. Now, I'll just temporarily lower the price of the item, if they tell me they intend to buy. I should check and see whether lowered prices take immediate effect -- just in case.