I can't speak for the Debian Testing version of Firefox, but the versions in Debian Unstable only suggest pulseaudio, and I've found a reliable means of getting Firefox 60+ to produce sound with apulse.
Install apulse and patchelf then cd /usr/lib/firefox/ or cd /usr/lib/firefox-esr/ and run(might be word wrapped, it its one line): sudo patchelf --set-rpath /usr/lib/i386-linux-gnu/apulse/ libxul.so You will probably need to adjust the i386 part of the path if your running 64-bit x86 or non-x86 versions of Debian. Can't speak for it fixing compatibility between Orca and espeakup since I don't use espeakup, but it allowed me to upgrade to Firefox newer than ESR 52 while keeping sound in the browser without having to install PulseAudio, and the only conflict I've run into with Orca and SBL is that Orca will speak over SBL even when I'm not in the terminal, but that only happens when say I switch to the terminal while Firefox is loading pages or while Orca/Firefox are trying to catch up with keystrokes. Can't gaurantee there aren't other problems with not having PulseAudio, but this resolved the only issue I've ever had to suggest there might be value in installing PulseAudio. -- Sincerely, Jeffery Wright Bachelor of Computer Science President Emeritus, Nu Nu Chapter, Phi Theta Kappa.