Full Unicode support for MAPI interfaces: New support for MAPISendMailW.Added a policy engine that allows customized Thunderbird deployments in enterprise environments, using Windows Group Policy or a cross-platform JSON file.On Windows a 64bit installer and MSI package are now available, see the Thunderbird for Organisations page for details.Preference needs to be set (and possily also needs to be set to false) Language packs can now be selected in the Advanced Options.File link attachments can now be linked to again instead of uploading them again.Thunderd 78 completely changes the formats of address books and they will not be 'downgraded' should you use this proceedure. However, Thunderbird 68.5 implements non-reversible changes to password storage. At the time of introducing this change there are no known incompatabilities with using an upgraded profile with an older version of Thunderbird, other than add-ons which may need to be removed and correct versions for the version of Thunderbird in use installed. If you have done this, you must change the default profile Thunderbird uses when it starts. I need to use my old profile and I clicked the new profile button! To downgrade to you will need to use the procedures at Dedicated profile per Thunderbird installation.

What happens to my profile if I downgrade to a previous version of Thunderbird If you have already manually created separate profiles for different installations, you will not notice the change. I already use separate profiles for my different Thunderbird installations

Directions are available in the Using multiple profile acticle. You can use the Profile Manager for each installation, to set a new default profile. Can I change which Thunderbird install uses my previous profile? Any previous profile data is saved and associated with the first Thunderbird installation that was opened after this change. You will not lose any personal data or customizations.