hi, i am using Firefox 78.5.0esr (32-bit) on my Raspberry Pi 4 (with 4GB). since the December 2020 update, Raspberry Pi OS is using PulseAudio as top overlay for ALSA, and Firefox 78.5.0esr does not play audio for some videos anymore. the maintainers of Raspberry Pi OS told me that it is not an issue of them, it must be an issue of Firefox. they told, it is maybe an issue related to bug #1422073: [https://bugzilla.mozilla.org/show_bug.cgi?id=1422073 no audio unless pulseaudio is already running] but none of the suggestions there helped me. here a link to a video that does not play audio in firefox, but play audio in chromium browser. https://www.youtube.com/watch?v=4Wrc4fHSCpw i, tried to clean cache, reset preferences, removed add-ons, made a new clean installation on a new clean system, but nothing helped. all the time the same behavior - some videos does not play with audio in firefox, others do. ''Raspberry Pi OS is an 32-bit opperating system for Raspberry Pi that has an ARM cpu, for those who don't know, what i am talking from.'' https://www.raspberrypi.org https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=293746