Toolbar treats .xxx domains as search queries rather than web site addresses.
When you type a domain name into the Google Toolbar — e.g. DNW.com — it takes you directly to the URL rather than Google’s search page.
The same thing happens when you type in most top level domain names, save for a few examples such as .cat.
But for now, .xxx is in the same category as .cat. If you type in casting.xxx, the toolbar brings you to Google’s search results page for casting.xxx.
For me, the first search result is the actual web site.
My guess is Google will selectively add auto-redirect to new top level domains to its search bar, but it might wait for them to get critical mass first.
Google Toolbar Discontinued says
That’s because Google Toolbar is discontinued. They will not update the change for the new domain extensions.
http://www.ghacks.net/2011/07/21/google-toolbar-support-for-firefox-5-discontinued/