It has long annoyed me that I couldn’t control the order my mail accounts are listed in the left pane in Mozilla Thunderbird.
In the end I decided to just edit my ~/.mozilla-thunderbird/default.xxx/prefs.js file to get it right, and after several unsuccessful attempts I found out how easy it is.
Open your prefs.js file in an editor and find a line like
The number of accounts depend on how many you have created while you have used that profile.
Anyway, just reorder the list. You’ll have to find the definition of each account to identify it, but it is not that hard.
Too bad there isn’t a GUI user interface for this.