[1] http://metadata.ftp-master.debian.org/changelogs/main/f/firefox-esr/firefox-esr_52.0.1esr-1_changelog
[2] https://www.mozilla.org/en-US/firefox/organizations/faq/
As temporary workaround you could use firefox-esr, it is build with
--enable-alsa since 52.0.1esr-1 [1] and will be supported untill Q1/Q2
2018 [2].
