A Google Chrome Extension to easily preview a bootstrap site with a bootswatch theme.
You can install the chrome extension from the Chrome Web Store
Once the extension is installed, you will see the extension's icon showing on the right of the address bar. Browse to the site you wish to preview. Click on the extension icon. The following popup will show. Select the desired theme either by modifying the drop down or click on the thumbnail image. Click "Apply Theme" button to inject the them to current page.
Information on how the extension was built can be found here.