New MP3 file fault

We're going to need a lot more detail than that to help. What service/site are you trying to upload them to? When you say you can't...what happens? Error message?

Hello. It is to Podbean, my podcast host. I am using Firefox. This must be a Firefox issue

Is it possible to try with IE or Edge and see if you can narrow it down to Firefox?

Good point. I will have a try, thanks.

OK, I can upload it with Edge. It is either a Firefox problem or a collision between Firefox and Win10. I have noticed that it will not let me set Firefox as the default browser in settings. Have you experienced that? Could that be part of the problem?

Since the upload works with Edge but not with Firefox, Firefox is certainly implicated, but not necessarily an interaction between Firefox and Win10. Remember, you've done a clean install; lots for things have changed. Have you searched for problems uploading to Podbean? I found nothing related to Firefox, but you haven't mentioned an error message so I was somewhat limited in my search.

I did find reference to a firewall issue:
http://support.podbean.com/customer/...hen-uploading-

The "Fail to open the file. Please check if the file can be accessed." may be caused by a firewall setting which removes the CORS (cross domain) permission in http header.

If you are using the Microsoft firewall it's possible it grants default permissions to Edge that it does not grant other browsers. I know nothing about Microsoft's firewall - I use Kaspersky Internet Security - but I assume there is a set of options granting or limiting a program's level of authority. (In KIS it's called Application Control.) See if Firefox is being limited in some way that would prevent your upload.

OK, thanks for that, I will have a poke about and see if there is a problem there.

OK, and if the problem is that the default browser cannot be changed to Firefox for some reason then we are locked in a problem as a previous man said. Thanks.

If it was a firewall issue, all browsers would be affected. To me, Firefox has withered away and died. It used to be a quality browser, but that time has passed. Chrome has far surpassed it, so give Chrome a shot if you don't want to use Edge.