When Thunderbird is updated from a prior major version (e.g. 2.0 to 3.0), a Migration Assistant tab is displayed. Additionally, a "What's new" tab may be shown on a minor version update (e.g. 3.0.3 to 3.0.4).

Some users have reported that these tabs open all the time. This article presents some possible solutions and workarounds.

You are running two different versions of Thunderbird using the same profile

If you are accessing the same profile from two different versions of Thunderbird, the "What's new" tab will be displayed each time you start Thunderbird.

Possible Solution: Ensure both instances of Thunderbird are updated to the same version.

An extension is causing a conflict in Thunderbird

Possible Solution: Try starting in Troubleshoot Mode Thunderbird. If that resolves it, the problem is being caused by one of your extensions. Click Tools > Add-ons on the Thunderbird menu to disable or delete extensions.

A preference is being overridden

Some people have a user.js file. This file might contain preferences that are not required, but make Thunderbird think it is starting up a new version each time.

Possible Solution:

1. Shut down Thunderbird.
2. Locate the Profile directory (as explained in the Profiles - Where Thunderbird stores your messages and other user data article).
3. Locate the user.js file.
4. Examine the user.js file for the following entries:
   • user_pref("mailnews.ui.threadpane.version", "x");
   • user_pref("mailnews.start_page_override.mstone", "y");

(In both cases, "x" and "y" can be any number or sequence of numbers and letters.)

If either or both of the above lines exist, delete them and save the file. This should resolve the issue.