Chrome
Chrome marks the address bar with a crossed-out microphone, but only once a page has asked and been refused.
- Press the button on the page that needs your microphone. Nothing appears to happen, and that is the point: the attempt is what makes Chrome show its mark.
- Click the crossed-out microphone at the right-hand end of the address bar.
- Choose to always allow this site to use your microphone, then select Done.
- Reload the page and press the button again.
No mark in the address bar? Paste chrome://settings/content/microphone into it, find the site under "Not allowed to use your microphone", click it, and set Microphone to Allow.