Do know that Microsoft can and will change your hardware drivers. (happened to me 5mins after updating my sound card drivers.) Check in Device Manager to see if any changes have been made. https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/ Can try https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows and https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox and https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Further info : https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API might want to just check out the page/s https://www.google.ca/search?q=firefox+WebAudio+API&ie=utf-8&oe=utf-8&gws_rd=cr&dcr=0&ei=k5rpWc-wN8Ll0gK1vJiwDA Please let us know if this solved your issue or if need further assistance.

Thanks for having a look into my issue. However, none of your suggestions solved it. Microsoft provides hardware drivers for my USB Audio device (it´s a Philips SpeechMike) anyway, so it can´t change drivers I have installed (because I never did that). It´s just, WebAudio in Firefox works with 44kHz and 16kHz devices, but it does not work with 22kHz devices. Chrome works with all of them.