They have amended their affiliate agreement, effective July 1, 2013, with the following:
This means no more building Firefox or Chrome add-ons that do something nice, then hijack every link to Amazon's site by inserting the developer's affiliate ID, often replacing the affiliate ID in links on sites created by people that play fair.
https://affiliate-program.amazon.com/gp/associates/help/operating/compare
Quote
7. Except as agreed between you and us in a separate written agreement referencing this Participation Requirement, you will not use any Content or Special Link, or otherwise link to the Amazon Site, on or in connection with:
a. any client-side software application (e.g., a browser plug-in, helper object, toolbar, extension, or component or any other application executable or installable by an end user) on any device, including computers, mobile phones, tablets, or other handheld devices;
This means no more building Firefox or Chrome add-ons that do something nice, then hijack every link to Amazon's site by inserting the developer's affiliate ID, often replacing the affiliate ID in links on sites created by people that play fair.
https://affiliate-program.amazon.com/gp/associates/help/operating/compare
