There are several ways to open a page for design in the wireframe pane and add the tab to the wireframe pane.
Double-clicking a page in the Sitemap will open the page for design.
Click the Design Page button in the Sitemap toolbar to open the page for design.
To open the page in the wireframe pane, right-click on a page and choose Design Page.
Select a page in the Sitemap and press Enter to open the page for design.