Here's how it will work: Select commercials will send a signal to set-top boxes and connected devices like smartphones or tablets to display a "buy-now" link. Viewers will then be able to purchase an item or make a donation using their PayPal accounts.

writes in a blog post that his company is "a natural fit" for such a service, and PayPal's payment system is the "critical final piece of the puzzle" for truly interactive shopping using your TV.

Internal research from PayPal shows that half of television users are open to purchasing goods and services through their television, and 30 percent would use PayPal to complete those transactions, a large untapped market for television commerce.

Comcast will enable purchases directly through the remote control or a companion device such as a tablet or smartphone (likely running Comcast's mobile app). The cable provider also will allow advertisers to send "coupons" directly to the PayPal accounts of subscribers.