For: -webkit-radial-gradient(contain, red, blue) gecko -> radial-gradient(closest-side, red, blue) stylo -> -webkit-radial-gradient(center center, contain, red, blue) I have no idea which is expected... I suspect stylo one.

It seems different browsers give different answer for this: gecko: radial-gradient(closest-side, red, blue) stylo: -webkit-radial-gradient(center center, contain, red, blue) blink: -webkit-radial-gradient(center, ellipse contain, red, blue) edge : -webkit-radial-gradient(contain, red, blue) I guess all of them are effectively identical. I tried to unconditionally set cssGradient->mIsLegacySyntax if there is webkit-prefix, but it seems the serialization code in nsCSSValue doesn't handle this case correctly, and generates "-webkit-radial-gradient(closest-side, red, blue)", which is probably invalid as a legacy syntax.

Bug 1380259 fixes the serialization differences for computed values, but not for specified values. I am reopening this bug to track the work required to fix this for specified values.

I'll take care of this. Setting P1 because it is the last blocker for enabling more mochitests.

Comment on attachment 8893690 [details] Bug 1367299 - Allow -webkit-radial-gradient to be serialized in different way with stylo. https://reviewboard.mozilla.org/r/164812/#review170414

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/4289bf021340 Allow -webkit-radial-gradient to be serialized in different way with stylo. r=dholbert