Tip 4.28: How to customize what clicking the X button does to a tool window or tool window tab group
“Visual Studio Tips, 251 ways to improve your Productivity in Visual Studio“, courtesy of ‘Sara Ford’
On the Tools–Options–Environment–General page, you’ll find the Close Button Affects Active Tool Window Only check box. The following screen shot shows a snapshot of two tool window tabs docked together, with the close button circled.
If you want only Solution Explorer to close when pressing the X button, enable the option. Otherwise, both tool windows will close.
Happy Programming! =)