Currently only supported by Firefox (as of 49.0), according to Mozilla [1]. Interestingly, it's being used by the BBC [2], who have reported a 10.8% reduction

Currently only supported by Firefox (as of 49.0), according to Mozilla [1]. Interestingly, it's being used by the BBC [2], who have reported a 10.8% reduction in 304 responses as a result [3]. Google have also stated their intention to use it (comment 11 in the same Chromium ticket). [1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Ca... [2] https://mybbc.files.bbci.co.uk/notification-ui/2.6.8-mvt//svg/setting.svg https://mybbc.files.bbci.co.uk/notification-ui/2.6.8-mvt//sv... [3] https://bugs.chromium.org/p/chromium/issues/detail?id=611416 https://bugs.chromium.org/p/chromium/issues/detail?id=611416