php download management - netscape/mozilla bug

[Freddy]

I am using the script as below, but there is a problem, in Netscape, and
Mozilla Firebird, a .php is added to the filename when the user is prompted
to save, it's ok in Internet Explorer and Opera though:

$filename="/home/myUserName/filename.exe";
header("Content-Disposition: attachment; filename=filename.exe");
header("Content-Type: application/octet-stream");
header("Content-Length: ".@filesize("$filename"));
readfile("$filename");

This works fine, other than on Mozilla Firebird and Netscape, it wants to
save as filename.exe.php
I've noticed if I make the download link download.php?anyvariable=anyvalue,
the .php IS NOT added however, so I use that to temporarily stop the
problem.
Can anyone suggest what I maybe doing wrong.

Thanks.