Sound from web page once visited persists at startup despite cookies being deleted
Greetings. Each time I open Firefox 76.0.1 on my iMAC OS 10.14.6 I have to listen a minute or so to frog calls. The problem began after I visited this page, which is the source of the sound: http://www.californiaherps.com/frogs/pages/p.regilla.sounds.html. To try to fix this, I've deleted all cookies and long ago closed the page with the frog call on it. Unfortunately, I sent this URL to a friend who subsequently developed the same problem. She is on a different browser, I think Chrome, and has Microsoft OS.
MalwareBytes can detect no problem with my system. How do I rid my Firefox of these frog calls? This does not happen when I open Safari or Chrome but I like using Firefox better.
Thanks in advance for your help, Susan