This article is about Thunderbird's profile folder.See also Profile folder - Firefox and Profile folder - Sea Monkey.The workaround is to install version 38.5.0 and then upgrade.However, that does not let you choose a specific version.The easiest way to resolve such problems is to restart your computer.Once the computer starts up again: Some programs that can interfere with Firefox are set to start up automatically when you start your computer.The first time you start Thunderbird it will automatically create a profile in a default location if it does not already exist.
I don't have any other copies running but I can't get rid of this. You may have to go directly to the Thunderbird website and download / install the newer version of Thunderbird, the newest version is 6.0.2.
Rebuilding the Global Database re-indexes messages and address book cards.
Not sure if this is the right place or not but last week, everytime I launched TB, it gave me this message: "Software update Failed: The update could not be installed. Thx When you get the "Thunderbird is already running" message, press the Ctrl Shift Esc keys to bring up task manager, under the process tab look to see if Thunderbird is running, if so click on the Thunderbird process then click End Process at the bottom right of task manager, then try to install the update.
Its also possible to keep the current version, and do a custom installation of a older version in a different directory to see if your problem is due to the latest version of Thunderbird or not.
See this article if you want to go back to an old version of Firefox.
Thunderbird stores all personal data such as messages, address books and configuration settings in an OS folder called the profile.