If the mp3 is embedded, Firefox will insist on using a plugin on my system, but not for links. In Options > Applications, you should be able to set Firefox to use a helper application for linked mp3.

From my original query: "Regardless of settings in "options", ....". I have tried every permutation. Thank you, though. Now, I just paste the links into winamp, a minor annoyance. I've done nothing to diagnose, not even tested it against an alternative player. Know of any relevant about:config entries? I'm thinking of downgrading until I get in front of the breakage and comparing entries in the respective files. Alternatively, if web sites don't complain, problem solved ...well, maybe.

See also:

• http://kb.mozillazine.org/File_types_and_download_actions
• https://support.mozilla.org/kb/Managing+file+types

I reiterate that I have tried every setting available within ff12. All I did was install over an existing version, making no changes in profile. Your second link, though, does contain evidence that later versions are broken so I can stop trying to diagnose this pig and roll back to a version that works until I can figure this one out. Thanks