diff --git a/toolkit/mozapps/extensions/LightweightThemeManager.jsm b/toolkit/mozapps/extensions/LightweightThemeManager.jsm
index f083de1945f..c2e22669f60 100644
--- a/toolkit/mozapps/extensions/LightweightThemeManager.jsm
+++ b/toolkit/mozapps/extensions/LightweightThemeManager.jsm
@@ -77,7 +77,8 @@ __defineGetter__("_ioService", function () {
 var LightweightThemeManager = {
   get usedThemes () {
     try {
-      return JSON.parse(_prefs.getCharPref("usedThemes"));
+      return JSON.parse(_prefs.getComplexValue("usedThemes",
+                                               Ci.nsISupportsString).data);
     } catch (e) {
       return [];
     }
@@ -297,7 +298,10 @@ function _updateUsedThemes(aList) {
   if (aList.length > MAX_USED_THEMES_COUNT)
     aList.length = MAX_USED_THEMES_COUNT;
 
-  _prefs.setCharPref("usedThemes", JSON.stringify(aList));
+  var str = Cc["@mozilla.org/supports-string;1"]
+              .createInstance(Ci.nsISupportsString);
+  str.data = JSON.stringify(aList);
+  _prefs.setComplexValue("usedThemes", Ci.nsISupportsString, str);
 
   _observerService.notifyObservers(null, "lightweight-theme-list-changed", null);
 }
diff --git a/toolkit/mozapps/extensions/test/unit/test_LightweightThemeManager.js b/toolkit/mozapps/extensions/test/unit/test_LightweightThemeManager.js
index edfc6fe6066..36cb5803dc5 100644
--- a/toolkit/mozapps/extensions/test/unit/test_LightweightThemeManager.js
+++ b/toolkit/mozapps/extensions/test/unit/test_LightweightThemeManager.js
@@ -122,6 +122,41 @@ function run_test() {
   do_check_eq(ltm.usedThemes.length, 0);
   do_check_eq(ltm.currentTheme, null);
 
+  // Use chinese name to test utf-8, for bug #541943
+  var chineseTheme = dummy("chinese0");
+  chineseTheme.name = "中文0";
+  chineseTheme.description = "中文1";
+  ltm.currentTheme = chineseTheme;
+  do_check_eq(ltm.usedThemes.length, 1);
+  do_check_eq(ltm.currentTheme.name, "中文0");
+  do_check_eq(ltm.currentTheme.description, "中文1");
+  do_check_eq(ltm.usedThemes[0].name, "中文0");
+  do_check_eq(ltm.usedThemes[0].description, "中文1");
+  do_check_eq(ltm.getUsedTheme("chinese0").name, "中文0");
+  do_check_eq(ltm.getUsedTheme("chinese0").description, "中文1");
+
+  // This name used to break the usedTheme JSON causing all LWTs to be lost
+  var chineseTheme1 = dummy("chinese1");
+  chineseTheme1.name = "植物大战僵尸~最爱";
+  chineseTheme1.description = "植物大战僵尸~最爱";
+  ltm.currentTheme = chineseTheme1;
+  do_check_neq(ltm.currentTheme, null);
+  do_check_eq(ltm.usedThemes.length, 2);
+  do_check_eq(ltm.currentTheme.name, "植物大战僵尸~最爱");
+  do_check_eq(ltm.currentTheme.description, "植物大战僵尸~最爱");
+  do_check_eq(ltm.usedThemes[1].name, "中文0");
+  do_check_eq(ltm.usedThemes[1].description, "中文1");
+  do_check_eq(ltm.usedThemes[0].name, "植物大战僵尸~最爱");
+  do_check_eq(ltm.usedThemes[0].description, "植物大战僵尸~最爱");
+
+  ltm.forgetUsedTheme("chinese0");
+  do_check_eq(ltm.usedThemes.length, 1);
+  do_check_neq(ltm.currentTheme, null);
+
+  ltm.forgetUsedTheme("chinese1");
+  do_check_eq(ltm.usedThemes.length, 0);
+  do_check_eq(ltm.currentTheme, null);
+
   do_check_eq(ltm.parseTheme("invalid json"), null);
   do_check_eq(ltm.parseTheme('"json string"'), null);
 
@@ -145,6 +180,14 @@ function run_test() {
   data.id = [];
   do_check_eq(roundtrip(data), null);
 
+  // Check whether parseTheme handles international characters right
+  var chineseTheme2 = dummy();
+  chineseTheme2.name = "植物大战僵尸~最爱";
+  chineseTheme2.description = "植物大战僵尸~最爱";
+  do_check_neq(roundtrip(chineseTheme2), null);
+  do_check_eq(roundtrip(chineseTheme2).name, "植物大战僵尸~最爱");
+  do_check_eq(roundtrip(chineseTheme2).description, "植物大战僵尸~最爱");
+
   data = dummy();
   data.unknownProperty = "Foo";
   do_check_eq(typeof roundtrip(data).unknownProperty, "undefined");
@@ -333,4 +376,21 @@ function run_test() {
   ltm.forgetUsedTheme("x2");
   do_check_eq(ltm.usedThemes.length, 0);
   do_check_eq(ltm.currentTheme, null);
+
+  // Test whether a JSON set with setCharPref can be retrieved with usedThemes
+  ltm.currentTheme = dummy("x0");
+  ltm.currentTheme = dummy("x1");
+  prefs.setCharPref("lightweightThemes.usedThemes", JSON.stringify(ltm.usedThemes));
+  do_check_eq(ltm.usedThemes.length, 2);
+  do_check_eq(ltm.currentTheme.id, "x1");
+  do_check_eq(ltm.usedThemes[1].id, "x0");
+  do_check_eq(ltm.usedThemes[0].id, "x1");
+
+  ltm.forgetUsedTheme("x0");
+  do_check_eq(ltm.usedThemes.length, 1);
+  do_check_neq(ltm.currentTheme, null);
+
+  ltm.forgetUsedTheme("x1");
+  do_check_eq(ltm.usedThemes.length, 0);
+  do_check_eq(ltm.currentTheme, null);
 }