When a visitor types the domain web address into their browser, the request goes to a server where a script redirects the visitor to the destination URL that you have designated. In that process, the original domain name is dropped so the domain name will not stay in the browser's address window.
You can however choose the masked forwarding option to keep your domain name as the address displayed in the web browser.
Note: Domain forwarding is available only in Yahoo! Domains and Yahoo! Business Email plans.