You should now see a Debug menu in Safari, to the right of the Help menu (not to be confused with the Develop menu). In this menu, disable “Use Multi-process Windows” by selecting it (when it’s disabled, it will no longer have a checkmark next to it).

By having an Apple ID serve every function related to Apple — operating system, purchasing, and cloud-stored data — our friends in Cupertino may have bitten off too much. Simplicity is a wonderful concept, and we support it fully. Apple’s integration of the Apple ID into Lion shows how well it can be done as an adjunct and support, while allowing multiple identities in one place. If the company could only bring that same level of consideration to the broader use of Apple IDs, it would make many of us a little more sane.