diff --git a/mozilla/modules/libpref/src/init/all.js b/mozilla/modules/libpref/src/init/all.js
index 7b809c8daa8..ae2e1b8f744 100644
--- a/mozilla/modules/libpref/src/init/all.js
+++ b/mozilla/modules/libpref/src/init/all.js
@@ -590,6 +590,15 @@ pref("network.IDN.whitelist.tw", true);
 pref("network.IDN.whitelist.info", true);
 pref("network.IDN.whitelist.museum", true);
 
+// If a domain includes any of the following characters, it may be a spoof 
+// attempt and so we always display the domain name as punycode. This would 
+// override the settings "network.IDN_show_punycode" and 
+// "netword.IDN.whitelist.*".
+// The list currently contains the characters:
+// U+2044 FRACTION SLASH
+// U+2215 DIVISION SLASH
+pref("network.IDN.blacklist_chars", "⁄∕");
+
 // This preference specifies a list of domains for which DNS lookups will be
 // IPv4 only. Works around broken DNS servers which can't handle IPv6 lookups
 // and/or allows the user to disable IPv6 on a per-domain basis. See bug 68796.