According to https://developer.mozilla.org/en-US/docs/Web/CSS/image-orientation, this property is being unshipped from images-4, and no other browsers support it. Should stylo really support that one, or should gecko remove its support of it?

CSSWG recently discussed about this property during the Tokyo F2F meeting, and resolved to deprecate <angle> value of the property, but keep from-image keyword value and add a none value. [1] That says, we probably still want to keep the property. It doesn't seem to me implementing this property to Gecko's behavior is particular hard for the style system, and given the spec hasn't been updated to include the new "none" value, I think it makes sense to just move forward with what Gecko currently does. [1] http://logs.glob.uno/?c=w3%23css&s=21+Apr+2017&e=21+Apr+2017&h=image-orientation#c190623

image-orientation support in stylo was added in bug 1341758. Was there something missing from that, that's still causing some test_value_storage.html failures?

parse+serialize should be idempotent for 'image-orientation: 0deg flip' - got "", expected "0deg flipped" serialize+parse should be identity transform for 'image-orientation: 0deg flip' - got "0deg", expected "0deg flip" parse+serialize should be idempotent for 'image-orientation: 90deg flip' - got "", expected "90deg flipped" serialize+parse should be identity transform for 'image-orientation: 90deg flip' - got "0deg", expected "90deg flip" parse+serialize should be idempotent for 'image-orientation: 180deg flip' - got "", expected "180deg flipped" serialize+parse should be identity transform for 'image-orientation: 180deg flip' - got "0deg", expected "180deg flip" parse+serialize should be idempotent for 'image-orientation: 270deg flip' - got "", expected "270deg flipped" serialize+parse should be identity transform for 'image-orientation: 270deg flip' - got "0deg", expected "270deg flip" parse+serialize should be idempotent for 'image-orientation: flip' - got "", expected "0deg flipped" serialize+parse should be identity transform for 'image-orientation: flip' - got "0deg", expected "0deg flip" parse+serialize should be idempotent for 'image-orientation: 0grad flip' - got "", expected "0grad flipped" serialize+parse should be identity transform for 'image-orientation: 0grad flip' - got "0deg", expected "0deg flip" parse+serialize should be idempotent for 'image-orientation: 100grad flip' - got "", expected "100grad flipped" serialize+parse should be identity transform for 'image-orientation: 100grad flip' - got "0deg", expected "90deg flip" parse+serialize should be idempotent for 'image-orientation: 200grad flip' - got "", expected "200grad flipped" serialize+parse should be identity transform for 'image-orientation: 200grad flip' - got "0deg", expected "180deg flip" parse+serialize should be idempotent for 'image-orientation: 300grad flip' - got "", expected "300grad flipped" serialize+parse should be identity transform for 'image-orientation: 300grad flip' - got "0deg", expected "270deg flip" parse+serialize should be idempotent for 'image-orientation: 0rad flip' - got "", expected "0rad flipped" serialize+parse should be identity transform for 'image-orientation: 0rad flip' - got "0deg", expected "0deg flip" parse+serialize should be idempotent for 'image-orientation: 1.57079633rad flip' - got "", expected "1.5707964rad flipped" serialize+parse should be identity transform for 'image-orientation: 1.57079633rad flip' - got "0deg", expected "90deg flip" parse+serialize should be idempotent for 'image-orientation: 3.14159265rad flip' - got "", expected "3.1415927rad flipped" serialize+parse should be identity transform for 'image-orientation: 3.14159265rad flip' - got "0deg", expected "180deg flip" parse+serialize should be idempotent for 'image-orientation: 4.71238898rad flip' - got "", expected "4.712389rad flipped" serialize+parse should be identity transform for 'image-orientation: 4.71238898rad flip' - got "0deg", expected "270deg flip" parse+serialize should be idempotent for 'image-orientation: 0turn flip' - got "", expected "0turn flipped" serialize+parse should be identity transform for 'image-orientation: 0turn flip' - got "0deg", expected "0deg flip" parse+serialize should be idempotent for 'image-orientation: 0.25turn flip' - got "", expected "0.25turn flipped" serialize+parse should be identity transform for 'image-orientation: 0.25turn flip' - got "0deg", expected "90deg flip" parse+serialize should be idempotent for 'image-orientation: 0.5turn flip' - got "", expected "0.5turn flipped" serialize+parse should be identity transform for 'image-orientation: 0.5turn flip' - got "0deg", expected "180deg flip" parse+serialize should be idempotent for 'image-orientation: 0.75turn flip' - got "", expected "0.75turn flipped" serialize+parse should be identity transform for 'image-orientation: 0.75turn flip' - got "0deg", expected "270deg flip" parse+serialize should be idempotent for 'image-orientation: -45deg flip' - got "", expected "-45deg flipped" serialize+parse should be identity transform for 'image-orientation: -45deg flip' - got "0deg", expected "270deg flip" parse+serialize should be idempotent for 'image-orientation: 65deg flip' - got "", expected "65deg flipped" serialize+parse should be identity transform for 'image-orientation: 65deg flip' - got "0deg", expected "90deg flip" parse+serialize should be idempotent for 'image-orientation: 400deg flip' - got "", expected "400deg flipped" serialize+parse should be identity transform for 'image-orientation: 400deg flip' - got "0deg", expected "0deg flip"

Xidorn explained that we should just do what Gecko does.

It seems this has been fixed.