• You forgot to convert the text to a regexp pattern.
• You only replace the first instance.
• And since I'm already changing the line, I'll remove the useless use of map.

$text =~ s/\Q$_\E/$fixers{$_}/g
   for keys %fixers;
[download]

It could still be improved if it's going to be done repeatedly.

my ($re) = map qr/$_/,
           join '|',
           map quotemeta,
           keys %fixers;

while (...) {
   ...
   $text =~ s/$re/$fixers{$_}/g
      for keys %fixers;
   ...
}
[download]

Or even better for pre-5.10

use List::Regexp qw( );

my $re = List::Regexp->new()->list2re( keys %fixers );

while (...) {
   ...
   $text =~ s/$re/$fixers{$_}/g
      for keys %fixers;
   ...
}
[download]