Heads-up for you Thunderbird users that there’s a known bug with Thunderbird where it generates an empty Thunderbird folder in your home directory. I think there were some xdg changes that may have caused this, but still a known issue for now. Track it here :
I noticed this too, not a big problem as it works as usual
Didn’t notice it until now, but there is actually a new Thunderbird folder in my home directory 
Hmm… it would seem there is no mysterious empty ~/Thunderbird directory with Betterbird (or ~/Betterbird for that matter).
I use FireDragon and Firefox. Same bug. All Mozilla-based apps probably have the same bug due to the XDG directory standardization switch.
Betterbird is based in Thunderbird ESR. Maybe this issue is only there in Thunderbird Release?