The default is 'allow everything' You can change a setting to block third party cookies. This gets you similar treatment of cookies as was the default in safar

The default is 'allow everything' You can change a setting to block third party cookies. This gets you similar treatment of cookies as was the default in safari 1-10. Safari 11 still blocks third party cookies by default, but has 'Intelligent Tracking Protection' as an additional filter on top of it. ITP blocks/limits certain uses of first-party cookies. Firefox has no analogous option. Either cookies are off, or all uses of first party cookies are allowed.