The deal with coupons.com is that they make a registry entry/change to limit the number of times a coupon was printed. No registry, no work. I don't know if that has changed recently or not. Even doing a Windows restore point prior to printing their coupons then rolling back after didn't work, supposedly. If I recall correctly I couldn't print to a .pdf printer, only a physical printer. Coupons.com did work with Firefox in Windows so it wasn't I.E. only. I don't think it worked is OSX at the time either, just Windows.
Edit: I just checked and Mac is supported now. Linux is not. It'd be interesting to hear how the Wine based emulators or VMs running Windows fare.