diff --git a/toolkit/content/tests/widgets/test_timepicker.xul b/toolkit/content/tests/widgets/test_timepicker.xul
index d1b1cad37842..ddf43b4aa65d 100644
--- a/toolkit/content/tests/widgets/test_timepicker.xul
+++ b/toolkit/content/tests/widgets/test_timepicker.xul
@@ -43,6 +43,10 @@ function testtag_timepicker()
   tp.value = testtag_gettimestring(thour, tminute, tsecond);
   testtag_comparetime(tp, testid + "set value", thour, tminute, tsecond);
 
+  var numberOrder = /^(\D*)\s*(\d+)(\D*)(\d+)(\D*)(\d+)\s*(\D*)$/;
+  var fdt = new Date(2000,0,1,16,7,9).toLocaleFormat("%X");
+  is(tp.is24HourClock, Number(fdt.match(numberOrder)[2]) > 12, "is24HourClock");
+
   // check that setting the dateValue property works
   tp.dateValue = today;
   testtag_comparetime(tp, testid + "set dateValue", thour, tminute, tsecond);
diff --git a/toolkit/content/widgets/datetimepicker.xml b/toolkit/content/widgets/datetimepicker.xml
index 6bc410dab6a0..aee5798ae3b3 100644
--- a/toolkit/content/widgets/datetimepicker.xml
+++ b/toolkit/content/widgets/datetimepicker.xml
@@ -246,12 +246,12 @@
            extends="chrome://global/content/bindings/datetimepicker.xml#datetimepicker-base">
 
     <implementation>
-      <field name="is24HourClock" readonly="true">false</field>
-      <field name="hourLeadingZero" readonly="true">false</field>
-      <field name="minuteLeadingZero" readonly="true">true</field>
-      <field name="secondLeadingZero" readonly="true">true</field>
-      <field name="amIndicator" readonly="true">"AM"</field>
-      <field name="pmIndicator" readonly="true">"PM"</field>
+      <field name="is24HourClock">false</field>
+      <field name="hourLeadingZero">false</field>
+      <field name="minuteLeadingZero">true</field>
+      <field name="secondLeadingZero">true</field>
+      <field name="amIndicator">"AM"</field>
+      <field name="pmIndicator">"PM"</field>
 
       <field name="hourField">null</field>
       <field name="minuteField">null</field>