I have been using Thunderbird for several years to manage my numerous email accounts from different providers and I am delighted with this mail client that continues to improve every day.
One of the latest extraordinary improvements offered by Mozilla in this application is to keep a list of the last folders used to Move or Copy messages. Since I manage many accounts and also many Local Folders, that list seemed very useful to me, but it has the disadvantage of its low capacity so it fills up quickly and ends up being useless. My suggestion is to expand this list of 15 current items to 50 or 100. This will not affect anyone since everyone can have the ones they want or none, and it does not practically take up any extra space.
Speaking of those Recent Folders and as a result of a change of my Profile to another computer, I have been able to verify that this list, so useful in power, is not saved along with the Profile, producing a big surprise when I saw that at the new computer that list was empty. In this case my suggestion is that this list will be also saved as part of the profile.
In the meantime I would ask you to tell me in which file this List of Recent Folders is stored, in order to be able to also export this file.