From the spec ; none The pseudo-element is not generated. Stylo does not pseudo elements at all.  https://www.w3.org/TR/CSS21/generate.html#content
https://treeherder.mozilla.org/#/jobs?repo=try&revision=539ae2c3258394e9c6aa7f73a30dfb5a763ba22a I have no idea how to test this without checking whether animation was created on the pseudo element which has 'content:none'.
Hiro, is this a bug we need to fix in Stylo? Or a bug in Gecko's style system?
Tight, this is a gecko bug, stylo handles the case correctly.
Marking as part of documentation plan for intentional stylo differences, just in case this is fixed before stylo hits release.
Documented: https://developer.mozilla.org/en-US/docs/Web/CSS/::before#Quantum_CSS_notes https://developer.mozilla.org/en-US/docs/Web/CSS/::after#Quantum_CSS_notes https://developer.mozilla.org/en-US/docs/Web/CSS/content#Quantum_CSS_notes https://developer.mozilla.org/en-US/Firefox/Releases/57#Quantum_CSS_notes
Closing since this is a bug for the old style system.
Status: NEW → RESOLVED
Closed: Last year
Resolution: --- → WONTFIX
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