Return back the window has lost the actived

In visual script,
Step 1: In windowbrowser 1, open windowbrowser 2
Step 2: In windowbrowser 2, open windowbrowser 3(Now, windowbrowser 3 is actived)
Step 3: Come back windowbrowser 2 to do something(Now, windowbrowser 2 is actived)
Step 4: Call a .netscript
In my .netscript, I want to work with some control on windowbrowser 2
Scenario: In this time, for some reasons, the windowbrowser 2 is lost actived(another application is now has actived)
Step 5: Get HTML from windowbrowser 2, but its error because lose actived.

The question is, how I return back exactly the windowbrowser which lose actived by another application(In this case is windowbrowser 2)?

Thanks.