As already said, feature upgrading Windows does not require a new
installation of TB. However, the best option anyway with TB is to keep
one or more profile folders completely independent of the TB installation.
Before you do a fresh install of TB move (not copy) your profile folder
to another location, preferably not on the system drive.The new TB
installation will create a default, unused profile in the usual location
but you can just ignore that. Instead run the new TB version using only
a shortcut which points it to your profile folder.
You can have as many profile folders as you like, just create a separate
shortcut for each one. Add-ons are kept in the profile folder so this is
also an easy way to have a backup profile and test new add-ons w/o risk
to your regular profile.
The shortcut format is (eg):
"C:\Program Files\Mozilla Thunderbird\thunderbird.exe" -profile "<path
to profile folder>\Data\profile"