1.  ensure thunderbird is NOT running on old machine
  2. enter %appdata% in search window on task bar and press Enter key
   3.this should open windows file explorer in Appdata\roaming folder
  4. highlight the Thunderbird folder and copy to external media
  5. ensure thunderbird is installed on second computer and NOT running
  6. enter %appdata% in search window on task bar and press Enter key
  7.you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it
  8. start Thunderbird and all should be there 

Several Months ago I bought a new W11 HP laptop and successfully followed the following procedure provided by David to get my TB profile/data and all files and folders onto this new computer. Here is the link for moving a profile in Windows when installed in default location: https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer here is the info in brief steps: 1. ensure thunderbird is NOT running on old machine 2. enter %appdata% in search window on task bar and press Enter key 3.this should open windows file explorer in Appdata\roaming folder 4. highlight the Thunderbird folder and copy to external media 5. ensure thunderbird is installed on second computer and NOT running 6. enter %appdata% in search window on task bar and press Enter key 7.you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it 8. start Thunderbird and all should be there There were a few hiccups but it works great! I now want to make sure I am creating a back up copy to save on a flash drive just in case something happens. I followed steps 1-3 above and that should be my back up..RIGHT? I did that and saved it in a folder labeled TB back up Profile and a date. My old was was to just back up the TB profile folder alone but I think this one saves everything. (accounts, folders, Local etc. Have I done it right???