Upload Thunderbird Emails into Gmail

[pavel]

I use Gmail and enabled POP as per Gmail instructions. I also created
an account again per Gmail instructions in Thunderbird. I do not
donwload emails from Gmail. However, I need to upload legacy emails
into my Gmail account.

I understand that GMail Loader and gExodus do not preserve fields from
original emails correctly.

As per advice on some forums, I installed extension Mail Redirect at
https://addons.mozilla.org/addon.php?id=550. I tried this extension on
Thunderbird versions 1.5 and 1.5.02. It redirects all fields correctly
with the exception of From field and From Email. From field is shown
as from Me in Gmail's conversation view. In More Options, the sender
of the original email is shown correctly, however, at my Gmail address.

How do I get this extension to show From field correctly in
conversation view and show the sender's email in More Options view at
their email address and not at my gmail address?

Thank you. Pavel