Hello,
I've noticed the same issue. However, under LW 1.8, the "launch" button worked because all mp3 files "associated" themselves with QuickTime 5. After I upgraded to LW 2.5, all mp3 downloads now show up as "generic", no association to an application. Why this is happening in a newer version of LW is a mystery.

In order to play the mp3 file now, I have to manually start QuickTime, then open the file (under QT) in order for it to play. Otherwise, I must now double-click on the "generic" mp3 file where a window appears asking me which applic to "associate" it with. Once I do that, I'm able to here the file. From there on, I can "launch" (from LW Shared dir) to here the song since it now has association.

Seems like a bug in LW 2.5.5.