Reorder Firefox containers
When Firefox introduced the ability to sync containers, the order was different on every PC. To change the order, all you need to do is reorder the containers.json file located in the Users -> Roaming -> Mozilla -> Firefox -> Profiles -> (Look for the directory containing your containers.json)
C:\Users\{username}\AppData\Roaming\Mozilla\Firefox\Profiles\{find-directory-with-file)\containers.json
%USERPROFILE%\AppData\Roaming\Mozilla\Firefox\Profiles
MAKE A BACKUP BEFORE YOU CHANGE IT!!!!