Hi Fernando, that's pretty strange.

In Private Windows, Firefox does not use cached files or cookies from regular windows. Did you clear both of those (steps at the end if needed)?

In the past, not sure about now, private windows also would be more accepting of third party cookies since all cookies were temporary anyway. If you are restricting third party cookies in regular windows, you might try modifying those settings. This article will point you to that part of the Options page:

Websites say cookies are blocked - Unblock them

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that.

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page. Does that help?

Thank you Jeff for taking the time to reply. I agree it's quite strange.

I have cleared cache and cookies and restarted Firefox, but it doesn't seem to affect. Also, tried to change automatic play under permissions, which I had set to block audio and set it to allow audio and video; again, no improvement.

Regarding the level of protection against tracking is Standard.

I have to say the normal Youtube videos play ok, it's only Youtube Music which gives problems.

I think the next step would be to reset Firefox to see if that makes a difference.

Best

ftella said

I have to say the normal Youtube videos play ok, it's only Youtube Music which gives problems.

Hmm, I wonder whether there might be a problem with DRM for those "videos"? The support article on DRM is here: Watch DRM content on Firefox.

Thank you Rasmus and Jeff!

I have tried to follow Rasmus' instructions as they offered more options to play with.

I went to about:profiles and created a new profile. Without doing anything else, opened a new Firefox window with it and went to Youtube Music and it worked fine. Ok. Then checked the settings about Autoplay and they were set to "Block Audio".

I went back to my old profile; then installed the User Agent String Switcher extension and tried to set it up as you said. At first I didn't understood how it worked so I didn't set it as it should, so I opened the Console (Ctrl+Shift+K), reloaded the Youtube Music page and got what you can see in the "Console Output" screenshot.

Then went back to the User Agent Switcher extension and managed to set it correctly, (I think) like shown in the "User Agent" screenshot, applied and voilà! It worked. :D

Then went back to the User Agent extension and click on Reset; it automatically got set to Mozilla Firefox only; applied, refreshed the site and got astonished with the result (check "astonished" screenshot). Amazing. It looks very much like you said Rasmus: they make it to work only on Chrome and disregard the rest of browsers.

In any case, there must be something that is preventing it from working in my old profile, as in the new one it worked without having to use the User Agent extension. I can live with the User Agent extension or without Youtube Music (now that I know about this selfish (to say the least) behavior, but it would be nice to learn what makes the difference from one profile to the other. Do you have any idea? Maybe the Console tells you more than me.

Thanks again. Fernando

Hmm, your Web Console shows a CORS error for www.youtube.com meaning that the site you are on -- is it music.youtube.com? -- is being denied access to content from www.youtube.com because that is a different origin (host name).

Perhaps this is caused by modifying some settings. Could you check the referring site header settings in case it is one of those:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box above the list, type or paste referer and pause while the list is filtered

Anything customized (bolded) here?

You can try to create a cookie allow exception for involved domains.

• Options/Preferences -> Privacy & Security
  Cookies and Site Data: "Manage Permissions"

Thank you both!

When trying the about:config > referer nothing bolded showed.

I then added the two sites (https://music.youtube.com/ and https://www.youtube.com/ and restarted Firefox. Nothing changed in Youtube Music.

I started comparing the about:config of the old session with the one of the new session to see if there's something meaningful. I have not finished yet.

Cheers! Fernando

Hello again!

I have to say that I probably didn't look for "referer" in the right profile, as I started comparing the whole config with the new profile and I went down to referer, where I found one entry in bold (I think it was referer alone). I went down to referer removing any custom thing in bold that wasn't present in the new profile and stopping from time to time and rebooting to test if it was fixed. It only solved after removing the bolded referer entry.

Thank you all for the help!

Best regards, Fernando