Thank you for that explanation--I found Dialog Toolkit. I tried entering "4", and also "3", "2", and "1" (it was defaulted to 0), restarting Opera each time, and it made no difference, the plugin still crashed.
I also took a look at the new VLC 2.2.0 from VideoLAN, and it seems to be more complex than I want to tackle. My MEPIS 11 is based on debian "squeeze", and VLC 2.2.0 seems to be aimed at "wheezy". This has already caused you and gwen-dragon more trouble than it's worth. I'll just take a couple extra steps and open any mp3 file with Konqueror, and consider that something in Opera or MEPIS is busted, and let it go at that. Thanks very much to both of you!