well uhh its not doing what i want. its trying to go to %1 which (goes to vh1????)
i typed //return $brwsr(http://www.mirc.com)

when i //echo'ed your code...
your code returned:
error! when reading or key does not exist
C:\PROGRA~1\MOZILLA.ORG\FIREBIRD\MOZILL~1.EXE -url "%1"


Code:
alias regread {
  var %a = regread
  .comopen %a WScript.Shell
  if !$comerr {
    var %b =  $com(%a,RegRead,3,bstr,$1-)
    var %c = $com(%a).result
    .comclose %a
    if (%c != $null) return %c
    else goto error
  }
  :error
  return error! when reading or key does not exist
}

alias testregread {
  if (($os == 95) || ($os == 98) || ($os == ME)) {
    echo -s $regread(HKLM\Software\Microsoft\Windows\CurrentVersion\Version)
  }
  elseif (($os == NT) || ($os == 2K) || ($os == XP)) {
    echo -s $regread(HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductName)
  }
}
alias brwsr { run $regread(HKCR\http\shell\open\command\) $replace($+($chr(34),$chr(36),%1,$chr(34)),$1-,$1-) }