This site should really include Mozilla's position on the spec too. Google shipping some, potentially harebrained, idea in Chromium doesn't mean that Safari and Firefox MUST also ship it. There should be links to relevant entries from https://mozilla.github.io/standards-positions/ and https://webkit.org/standards-positions/
This is a good example of how the chromium monoculture hurts the web. It ends up being Google's way or highway.
EDIT: You can filter by features that both Firefox and Chrome support by tapping the Chrome icon. This takes the list from 63 entries to 29