When you update Firefox, your previous data should automatically carry over because every version of Firefox will be able to view the folder that your data is stored in. If you updated Firefox and are now missing some data (bookmarks, logins, passwords, etc), it's very likely that Firefox accidentally created a new default profile for you.

To fix that, see the Determine if Firefox has created a new profile section of the Recover lost or missing Bookmarks page.

Hope this helps.

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