my $ffox = 'C:\Program Files\Mozilla Firefox\firefox.exe';

$ffox =~ s/\\/\\\\/g; #Replacing single \ with double \\

$ffox =~ s/\ /\\ /g; # Adding escape character before space

chop($firefoxVer);   # remove last \n chr.

$ffox =~ s/$/\\\"/g; # With the below two commands, massaging the command to become

$ffox =~ s/^/\\\"/g; # "C:\\Program\ Files\\Mozilla\ Firefox\\firefox.exe\"

$firefoxVer = $ffox.' --version|'; # Adding "version|" to the above command

$firefoxVer =~ s/$/\"/g;  # and make it look like:

$firefoxVer =~ s/^/\"/g;  # "\"C:\\Program\ Files\\Mozilla\ Firefox\\firefox.exe\" --version|"

open (IN, $firefoxVer) or die "Couldn't fork - $!\n"; ==> Fails