diff --git a/extensions/pref/autoconfig/src/prefcalls.js b/extensions/pref/autoconfig/src/prefcalls.js
index 74a36b482ace..1f0416c3052c 100644
--- a/extensions/pref/autoconfig/src/prefcalls.js
+++ b/extensions/pref/autoconfig/src/prefcalls.js
@@ -114,6 +114,12 @@ function getPref(prefName) {
         switch (prefBranch.getPrefType(prefName)) {
             
         case prefBranch.PREF_STRING:
+            if (gIsUTF8) {
+                const nsISupportsString = Components.interfaces.nsISupportsString;
+                let string = Components.classes["@mozilla.org/supports-string;1"]
+                                       .createInstance(nsISupportsString);
+                return prefBranch.getComplexValue(prefName, nsISupportsString).data;
+            }
             return prefBranch.getCharPref(prefName);
             
         case prefBranch.PREF_INT:
diff --git a/extensions/pref/autoconfig/test/unit/autoconfig-latin1.cfg b/extensions/pref/autoconfig/test/unit/autoconfig-latin1.cfg
index 688ef5458006..6b96c65fd05f 100644
--- a/extensions/pref/autoconfig/test/unit/autoconfig-latin1.cfg
+++ b/extensions/pref/autoconfig/test/unit/autoconfig-latin1.cfg
@@ -2,4 +2,5 @@
 // ©
 lockPref("_test.string.ASCII", "ASCII");
 lockPref("_test.string.non-ASCII", "日本語");
+lockPref("_test.string.getPref", getPref("_test.string.non-ASCII"));
 lockPref("_test.string.gIsUTF8", String(this.gIsUTF8));
diff --git a/extensions/pref/autoconfig/test/unit/autoconfig-utf8.cfg b/extensions/pref/autoconfig/test/unit/autoconfig-utf8.cfg
index 6a76dbf056c7..eec789942080 100644
--- a/extensions/pref/autoconfig/test/unit/autoconfig-utf8.cfg
+++ b/extensions/pref/autoconfig/test/unit/autoconfig-utf8.cfg
@@ -2,4 +2,5 @@
 
 lockPref("_test.string.ASCII", "UTF-8");
 lockPref("_test.string.non-ASCII", "日本語");
+lockPref("_test.string.getPref", getPref("_test.string.non-ASCII"));
 lockPref("_test.string.gIsUTF8", String(this.gIsUTF8));
diff --git a/extensions/pref/autoconfig/test/unit/test_autoconfig_nonascii.js b/extensions/pref/autoconfig/test/unit/test_autoconfig_nonascii.js
index b0b4a213be30..a42bc1219ff7 100644
--- a/extensions/pref/autoconfig/test/unit/test_autoconfig_nonascii.js
+++ b/extensions/pref/autoconfig/test/unit/test_autoconfig_nonascii.js
@@ -31,6 +31,7 @@ function run_test() {
       prefs: {
         "_test.string.ASCII": "UTF-8",
         "_test.string.non-ASCII": "日本語",
+        "_test.string.getPref": "日本語",
         "_test.string.gIsUTF8": "true"
       }
     }, {
@@ -38,6 +39,7 @@ function run_test() {
       prefs: {
         "_test.string.ASCII": "ASCII",
         "_test.string.non-ASCII": "日本語",
+        "_test.string.getPref": "日本語",
         "_test.string.gIsUTF8": "false",
       }
     }];