put a label on each with a filter and sort it by label

If you are talking about changing the order they appear in the folder pane there is an add on called Manually Sort Folders that will do what you want. Go to the add on page and do a search for it.

Im confused. Is it accounts or folders or email in the inbox you want to sort? If its folders there is an add-on, as Airmail said, that also sorts accounts, but folders and accounts are easy rename like [email protected], [email protected] 3-....... Just a warning thou just rename folders you created. And I saw that renaming the display-name of accounts didn't have any effect.