Firefox Extension Permissions

In the store description, the extension has a list of sites it requires full access to (why does it need access to all those Amazon sites?) and mentions full access to all visited sites as only optional. However, when trying to actually instal the extension, it askes for full access to all sites as required. The only optional permission is access in private mode. Why does the extension need default control over all visited websites? That seems like quite an overstep and makes the extension seem less secure, possibly creating a barrier for people to install it.