Go to a site that IE will remember form data from e.g. http://google.com enter some search terms in IE 7. Start up Firefox for the first time, go through the migration wizard select IE, browse to http://google.com attempt some of the same search terms that you did in IE 7. I don't get any autocomplete data.
See bug 355538 (passwords not imported) for current issues. Passwords and form data storage are the same in IE7 and the method of storage has changed.
This is a valid bug; if the underlying problem is the same it should be a duplicate.
Ok, cool. I wasn't sure if it should be resolved wontfix, dupe, or invalid honestly. There's no "can't fix". :)