Account order

You can change the order of your mail accounts in the folders pane by modifying prefs.js as described in this thread. The prefs.js file is found in your profile folder. If you have trouble figuring out which accounts are assigned to which account numbers in prefs.js, or if you try changing the order of accounts in prefs.js but the order displayed in Thunderbird's folders pane is not what you expected, see this thread for further information.