Although some Facebook posts are fluid when the data-width property is left blank or absent, others require this property to be set to render an appropriately sized iframe.
Unfortunately, this only allows an appropriately size iframe to be rendered in the first place, but does not allow the embed to become responsive. Facebook hardcodes the value given by data-width into inline styles elsewhere in the embed.
Although some Facebook posts are fluid when the data-width property is left blank or absent, others require this property to be set to render an appropriately sized iframe.
Unfortunately, this only allows an appropriately size iframe to be rendered in the first place, but does not allow the embed to become responsive. Facebook hardcodes the value given by data-width into inline styles elsewhere in the embed.