src/macosx/classes/sun/lwawt/macosx/CEmbeddedFrame.java

*** 143,152 ****
--- 143,162 ----
      // handleWindowFocusEvent is called for all applets, when the browser
      // becomes active/inactive. This event should be filtered out for
      // non-focused applet. This method can be called from different threads.
      public void handleWindowFocusEvent(boolean parentWindowActive) {
          this.parentWindowActive = parentWindowActive;
+         // If several applets are running in different browser's windows, it is necessary to
+         // detect the switching between the parent windows and update focusedWindow accordingly.
+         synchronized (classLock) {
+             if (parentWindowActive && focusedWindow != this &&
+                 (focusedWindow == null || (focusedWindow != null && !focusedWindow.isParentWindowActive()))) {
+                 // It looks like we have switched to another browser window, let's set focus to
+                 // the first applet in this window.
+                 focusedWindow = this;
+             }
+         }
          // ignore focus "lost" native request as it may mistakenly
          // deactivate active window (see 8001161)
          if (focusedWindow == this && parentWindowActive) {
              responder.handleWindowFocusEvent(parentWindowActive, null);
          }