Per the Amazon Ad Personalize setting:

> Because your selection above is managed through HTTP cookies, if you delete these cookies or use a different browser, you will have to make this same selection again.

Sigh. So you have to turn this on on every browser on every device.

It looks like the relevant cookies are ad-pref-session and apn-privacy. Perhaps syncing these (maybe only the latter one) would be just as effective as changing the setting through Amazon's site.

Of course there is little way of knowing how effective changing this setting is.