When Hibernate loads an object into a Session it creates a state snapshot of the current database state of the object, so that it can perform dirty checking against the snapshot.
As a read only object will never be modified, this snapshot is not needed and memory can be saved.
Session Manager saves and restores the state of all windows - either when you want it or automatically at startup and after crashes. Additionally it offers you to reopen (accidentally) closed windows and tabs. If you're afraid of losing data while..
Not perfect, but the best multiple-session-in-one-browser solution I know of: "CookieSwap is a Firefox/Mozilla extension that enables you to maintain numerous sets or "profiles" of cookies that you can quickly swap between while browsing."
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