The third party cookie blocking in Firefox is different from the feature available in Safari. Safari's policy is designed to block third-party cookies unless you already have a first-party relationship with the site. So, unless circumvented, it will block ad networks from tracking you but won't prevent things like the Facebook "like" button from working. The Firefox policy will prevent use of third-party cookies always, even for sites where you have a pre-existing relationship.
The Safari policy was designed to pick a tradeoff of privacy vs. compatibility that would let it be enabled by default. Since most users never change default settings, this arguably gives more privacy benefit to the typical user, at the expense of a bit more control for experts.
Side note: the Chrome third-party cookie blocking setting behaves roughly the same as that in Safari, but is not on by default, so it has less privacy impact than either the Safari or Firefox approaches.
The Safari policy was designed to pick a tradeoff of privacy vs. compatibility that would let it be enabled by default. Since most users never change default settings, this arguably gives more privacy benefit to the typical user, at the expense of a bit more control for experts.
Side note: the Chrome third-party cookie blocking setting behaves roughly the same as that in Safari, but is not on by default, so it has less privacy impact than either the Safari or Firefox approaches.