All minor points:

Get more debug information using the special variable, $!, when checking the success of open.

Using the 3-argument form of open is also a good practice: 

open my $FI, '<', 'fileExtensionList.txt or die "couldn't open input f
+ile: $!";

[download]

It doesn't look like you use your other filehandle, $FO.

Instead of using comments for your description, you could use POD: 

=head1 Description

FileExtP.pl will generate a list of files with incorrect
settings for "confirm open after download and "always show
extension"

=cut

[download]

That way, you can get info about your program from the commandline: 

$ perldoc FileExtP.pl

[download]

In reply to Re: tieregistry file ext search script critique by toolic
in thread tieregistry file ext search script critique by gebuh

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