On Firefox 11 you can migrate all data from Chrome but actually you can migrate from IE, Opera and Safari. Only that this is activated when Firefox is running for first time. I think this should be done when you want and not for the first time.

On Firefox 11 you can use this to import some data (currently bookmarks, history, cookies) from Google Chrome.
More items will be added in later Firefox versions

• Bookmarks > Show All Bookmarks > Import & Backup > Import Data from Another Browser