chromium and opera work with mictests.com, firefox fails

I use linux mint 20.1 When I try to use mictests.com on firefox, test fails. Firefox says this: Testing failed because your microphone could not capture any sounds. Please make sure your microphone is not muted and try again. arecord/aread work: arecord -f cd -d 20 --device="hw:0,0" cica.wav aplay cica.wav All other mic tests behave identical, do not work on firefox, but work on chromium/opera. I could not find any hint in the web. In the mean time solved, see my comment below. I assume, the fact, that I used chromium and opera to test the microphone fixed the error also in firefox. If somebody understands this kind of problem, it would be useful, if he/she enlightened us.