--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -5898,16 +5898,19 @@ nsWindow::ProcessMessage(UINT msg, WPARA
         // if it appears that the window's scaling is not what we expect.
         // This causes the prescontext and appshell window management code to
         // check the appUnitsPerDevPixel value and current widget size, and
         // refresh them if necessary. If nothing has changed, these calls will
         // return without actually triggering any extra reflow or painting.
         if (WinUtils::LogToPhysFactor(mWnd) != mDefaultScale) {
           ChangedDPI();
           ResetLayout();
+          if (mWidgetListener) {
+            mWidgetListener->UIResolutionChanged();
+          }
         }
       }
       break;
 
     case WM_ENTERSIZEMOVE:
     {
       if (mResizeState == NOT_RESIZING) {
         mResizeState = IN_SIZEMOVE;