What are profiles?

Thunderbird saves information such as messages, passwords and user preferences in a set of files called a profile. This profile is stored in a location separate from the Thunderbird applicationprogram files. More details on profiles can be found here.

What profile changes were made in Thunderbird 68?

Some users have multiple program installations of Thunderbird, each in separate applicationprogram folders. These separate Thunderbird installations previously shared a single profile by default. Starting with Thunderbird version 68, Thunderbird uses a dedicated profile for each program installation of Thunderbird (including Nightly and Beta. This makes Thunderbird more stable when switching between installations on the same computer, and also allows you to run different installations of Thunderbird at the same time.

You will not lose any personal data or customizations. Any previous profile data is saved and associated with the first Thunderbird installation that was opened after this change.

What are my options?

If you do nothing, your profile data will be different on each installation of Thunderbird.

Can I change which Thunderbird install uses my previously shared profile?

Yes. You can use the Profile Manager for each installation, to set a new default profile. Directions are available in the Profile Manager article. See also the Recover user data missing after Thunderbird update article.

What happens to my profile if I downgrade to a previous version of Thunderbird?

You should create a new profile to avoid corruption issues.

Starting with Thunderbird version 68, each Thunderbird installation requires a separate profile. Any previous profile data is saved and associated with the first Thunderbird installation opened after the change.

If you try to launch a Thunderbird installation with a profile that was last used in a more recent version, you'll see a warning that using an older version of Thunderbird can corrupt profile data such as xxxx:

Click the Create New Profile button to start Thunderbird with a new profile.

When you downgrade Thunderbird and use a new profile, any profile that was used in the higher version is still available in the Profile Manager, for use in a more recent version of Thunderbird.

Note: Downgrade protection can be overridden by launching Thunderbird through the command line with the --allow-downgrade parameter.

I already use separate profiles for my different Thunderbird installations

If you have already manually created separate profiles for different installations, you will not notice the change (this has been the recommended procedure on Nightly for a while).