No download button or dialogue appears to add a theme to Thunderbird even though Personas Plus has been installed and Thunderbird restarted.
I am using the latest version & build of Thunderbird as well as the latest Maxthon web browser. Please & thanks much.
الحل المُختار
What?
Perhaps the issue is you are using personas plus! It has not been updated to work with a version after 19. Mainly because it is no longer needed as personas were renamed as themes and themes to complete themes. so remove it and try using the themes from the add-on manager
On the toolbar 
then 
and select get add-ons. Themes are on the bottom right
All Replies (2)
الحل المُختار
What?
Perhaps the issue is you are using personas plus! It has not been updated to work with a version after 19. Mainly because it is no longer needed as personas were renamed as themes and themes to complete themes. so remove it and try using the themes from the add-on manager
On the toolbar then and select get add-ons. Themes are on the bottom right
Perfect. Thanks much, Matt.