Moving old Thunderbird and Firefox in to new setup

[Steven Rosenberg]

I think you have to go into the applications and point them to the
specific user file. When you do a new install, new user files are
created, and the applications point to those rather than anything you
bring over from your previous install.

Here are some Mozilla docs that I've used to do this in the past:

http://kb.mozillazine.org/Moving_your_profile_folder_-_Thunderbird

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
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Steven Rosenberg
http://stevenrosenberg.net/blog
http://blogs.dailynews.com/click