The IETF QUIC isn't finished. Periodically the Working Group thinks it has stopped fiddling with the low-level bit layout and is ready to focus on polish, then somebody finds a show stopper that means revisiting the low-level bits. Maybe 2020? They missed all their advisory target dates (July 2019) for actually writing documents, and that isn't the end by any means for a protocol like this.

So Firefox could at most support either Google QUIC (internal prototype, now obsolete, who cares?) or a random draft that may end up not resembling the final product. If they haven't decided to do either it doesn't seem like a big deal.