you need to implement deep linking concept to achieve bookmarking in flex application. By implementing the deep linking in flex application using BrowserManager class you can specify a different url for every state in flex application. Say you have a website in flex with Home, About and Contact states (pages). They can be opened directly using these urls

http://www.mywebsite.com/#home
http://www.mywebsite.com/#about
http://www.mywebsite.com/#contact

Here is the link that describes the concept of deep linking in actionscript 3.0

http://livedocs.adobe.com/flex/3/html/help.html?content=deep_linking_3.html