--- a/modules/libpref/src/nsPref.cpp
+++ b/modules/libpref/src/nsPref.cpp
@@ -442,30 +442,32 @@ NS_IMETHODIMP nsPref::CopyDefaultUnichar
 NS_IMETHODIMP nsPref::SetUnicharPref(const char *pref, const PRUnichar *value)
 {
   nsresult rv;
 
   nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv);
   if (NS_SUCCEEDED(rv)) {
     nsCOMPtr<nsISupportsString> theString = do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID, &rv);
     if (NS_SUCCEEDED(rv)) {
-      theString->SetData(nsDependentString(value));
+      nsAutoString val(value);
+      theString->SetData(val);
       rv = prefBranch->SetComplexValue(pref, NS_GET_IID(nsISupportsString), theString);
     }
   }
   return rv;
 }
 
 NS_IMETHODIMP nsPref::SetDefaultUnicharPref(const char *pref, const PRUnichar *value)
 {
   nsresult rv;
 
   nsCOMPtr<nsISupportsString> theString = do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID, &rv);
   if (NS_SUCCEEDED(rv)) {
-    theString->SetData(nsDependentString(value));
+    nsAutoString val(value);
+    theString->SetData(val);
     rv = mDefaultBranch->SetComplexValue(pref, NS_GET_IID(nsISupportsString), theString);
   }
   return rv;
 }
 
 NS_IMETHODIMP nsPref::GetLocalizedUnicharPref(const char *pref, PRUnichar **_retval)
 {
   nsresult rv;