By using NTLM authentication to access Alfresco WebDAV sites, the web browser can automatically log in.
When SSO is enabled, Internet Explorer will use your Windows login credentials when requested by the web server. Firefox and Mozilla also support the use of NTLM but you need to add the URI to the Alfresco site that you want to access to network.automatic-ntlm-auth.trusted-uris option (available through writing about:config in the URL field) to allow the browser to use your current credentials for login purposes.
The Opera web browser does not support NTLM authentication. The browser is detected and will be sent to the usual Alfresco logon page.
In this configuration, Alfresco must still store its own copy of your MD4 password hash. In order to remove this need and authenticate directly with a Windows domain controller, consider using the pass-through subsystem.