"The mp3 player sux "
mIRC doesnt have an mp3 player, it merely sends the request to windows to handle.
As KT pointed out, you are using a version of mIRC that had a bug with handling of default browser. Either upgrade to the current version, or look in the bug forum here where workarounds for that are posted.
Its your choice to use mIRC or not, but there's no need to be rude
