If the you select "Search the Web for..." from the Smart Tools menu, it searches the Internet using Yahoo! Search for anything related to the highlighted text and presents those web matches in a new window.

When you click any of the links in the new window, it navigates the prior window to the destination URL. If you want to see all the related results from Yahoo! Search, click "Show All Related Web Results".

Clicking "Show All Related Web Results" takes you to the Search result page and closes the window. You can navigate back using the browser back button.

Here's what it looks like in action: