What’s holding up the Firefox implementation? Parent select is one feature that xpath would’ve provided earlier than the adopted selector spec. Glad to see it coming over.
caniuse says that Firefox supports it but not by default -- it can be enabled via a flag. I guess they don't have confidence yet to turn it on by default.
Have to say, I'm very excited to see all the new additions CSS is getting lately. Things like this and the has: selector are going to make web development way better than before.
