Mozilla can be quite slow with certain features; for example work on U2F support hasn't even begun one year after a ticket was made (https://bugzilla.mozilla.org/show_bug.cgi?id=1065729). I'm not exactly holding my breath.
They've already tried to land the code to add brotli support but had to back it out because of an Android build failure. They're moving pretty quick on this. It helps that they already had brotli for WOFF so there is less review required.