As FunkyMonk already pointed out, you need to escape the backslash in your regular expression. Otherwise \x2f is interpolated as the hex character 2F, which is "/".

You could easily make this translation generic if there are other characters that might be escaped.

my $str = 'https:\x2F\x2Fwww.google.com\x2Faccounts\x2FCheckCookie?cht
+ml=LoginDoneHtml';

$str =~ s{\\x([0-9a-fA-F]{2})}{chr hex $1}eg;

print $str;
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- Miller