The problem may lie in the if statement it self.

if ($name = "firstname"){
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isn't checking anything it is assigning someting. You want

if ($name eq "firstname"){
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'=' assigns '==' is numerical comparisons and 'eq' is for string comparisons. (by design not by force)

If you did this with CGI you could do this:

use CGI;
use strict;
my %FORM;
map    {$FORM{$_} = 
        uri_unescape($cgi->param("$_"))} $cgi->param();
if ($FORM{firstname} eq '') {
      die print "must enter first name";
}
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or something along those lines, but you shouldn't die in CGI either. There are much more graceful and correct ways to handle it. So a super search for CGI Ovid and you should find loads of helpful information.