Firefox is GPLv3 compatible. It's quite likely that it will support this format - although, if it's the only major browser doing so, it will not be adopted by most web publishers.
I would be very surprised if Firefox added support. They have been very reluctant to include any additional image formats that weren't developed by Mozilla employees. See for example WebP and Jpeg2000.
Their reasons being things like added security risk, lack of demand, lack of support in other browsers, patent risk etc, which all apply just as much to this format.
The Mozilla Public License is GPLv3 compatible. Firefox also contains code that is under different licenses that is not GPLv3 compatible, and thus firefox is not GPLv3 compatible
Their reasons being things like added security risk, lack of demand, lack of support in other browsers, patent risk etc, which all apply just as much to this format.