the topic is not related to this issue, u should use another post so next guy asking here the same thing can retrieve it using google, like this: http://lmgtfy.com/?q=installing+mp3+plugin+fedora
reading here and there, i got that mp3 is not a free codec, so it is not released with fedora; if u want use closed codec u should use unofficial repo like fusion
i do not suggest you to use it if u are not very very familiar with fedora upgrades: the next upgrade u will have trouble having included rpmfusion and u will think back to my suggestion
u suggest you to play music with other codec like ogg, it's free
regards m.