--- a/content/html/content/src/HTMLInputElement.cpp
+++ b/content/html/content/src/HTMLInputElement.cpp
@@ -3910,17 +3910,17 @@ HTMLInputElement::PostHandleEvent(nsEven
       // control and as a result aVisitor.mEventStatus will already have been
       // set to nsEventStatus_eConsumeNoDefault. However, we know that
       // whenever the up/down arrow keys cause the value of the number
       // control to change the string in the text control will change, and
       // the cursor will be moved to the end of the text control, overwriting
       // the editor's handling of up/down keypress events. For that reason we
       // just ignore aVisitor.mEventStatus here and go ahead and handle the
       // event to increase/decrease the value of the number control.
-      if (!aVisitor.mEvent->mFlags.mDefaultPreventedByContent) {
+      if (!aVisitor.mEvent->mFlags.mDefaultPreventedByContent && IsMutable()) {
         StepNumberControlForUserEvent(keyEvent->keyCode == NS_VK_UP ? 1 : -1);
         aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
       }
     } else if (nsEventStatus_eIgnore == aVisitor.mEventStatus) {
       switch (aVisitor.mEvent->message) {
 
         case NS_FOCUS_CONTENT:
         {
@@ -4135,17 +4135,18 @@ HTMLInputElement::PostHandleEvent(nsEven
             if (mouseEvent->button == WidgetMouseEvent::eLeftButton &&
                 !(mouseEvent->IsShift() || mouseEvent->IsControl() ||
                   mouseEvent->IsAlt() || mouseEvent->IsMeta() ||
                   mouseEvent->IsAltGraph() || mouseEvent->IsFn() ||
                   mouseEvent->IsOS())) {
               nsNumberControlFrame* numberControlFrame =
                 do_QueryFrame(GetPrimaryFrame());
               if (numberControlFrame) {
-                if (aVisitor.mEvent->message == NS_MOUSE_BUTTON_DOWN) {
+                if (aVisitor.mEvent->message == NS_MOUSE_BUTTON_DOWN && 
+                    IsMutable()) {
                   switch (numberControlFrame->GetSpinButtonForPointerEvent(
                             aVisitor.mEvent->AsMouseEvent())) {
                   case nsNumberControlFrame::eSpinButtonUp:
                     StepNumberControlForUserEvent(1);
                     mNumberControlSpinnerSpinsUp = true;
                     StartNumberControlSpinnerSpin();
                     aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
                     break;