Code:
alias filterext {
  if ($isfile($2-)) {
    var %re = $+(/^\Q,$replacexcs($1,;,\E|\Q,\E,\E\\E\Q),\E$/)
    filter -ffg $qt($2-) nul %re
    echo -a * Found: $filtered
  }
}


/filterext <extensions> <file>

<extensions> should be a list of extensions you want to match like *.mp3;*.mpg;*.etc