1. Select the link for the .mp3 that you wish to download so that it opens in a new tab.
    
  2. Long press on the bar in the centre of the screen with the play/pause control, time elapsed and volume control. Select Save Audio…and the file will download. (Tested it myself and it works.)
  • Indeed. I use ublock origin’s logger on android to get the links to the media, if possible.

    Edit: Android FF doesn’t allow access to about:config. I have heard that it’s available on beta and/or nightly, but I use the stable/regular one. It also doesn’t have developer tools and the extensions are limited.