diff --git a/mozilla/widget/src/gtk2/nsWindow.cpp b/mozilla/widget/src/gtk2/nsWindow.cpp
index e2d645823e0..40aa65dea2e 100644
--- a/mozilla/widget/src/gtk2/nsWindow.cpp
+++ b/mozilla/widget/src/gtk2/nsWindow.cpp
@@ -435,6 +435,11 @@ NS_IMETHODIMP
 nsWindow::IsVisible(PRBool & aState)
 {
     aState = mIsVisible;
+    if(mIsTopLevel && mShell && !GTK_WIDGET_MAPPED(mShell)) {
+        /* we do not change mIsVisible to PR_FALSE here so we don't bother to
+           to change it back to PR_TRUE when the mShell is mapped again. */
+        aState = PR_FALSE;
+    }
     return NS_OK;
 }