I updated FireFox today like I normally do, but this time it refused to play sound. Sound was working everywhere else, so I figured that something related to the update broke it.1.
After minutes of searching, the FreeBSD forums had the solution2. Apparently this is due to the sndio daemon being installed, but disabled. You can read all the gory details at the forum link below, but enabling the sndiod service seems to work for now.