Where is the profile folder in the flatpak version of Thunderbird?

Hi, I just installed Elementary OS on a Dell M6800. The OS runs well, and I have multiple email accounts, so I installed Thunderbird from the Elementary AppCenter. It showed up as a flatpak install, but I went ahead. Now, in the past when I tried to replace the .default-release file with one from another machine and rename it with the new filename (which is what I've always done to transfer my multiple emails and address book), I went to the usual place, which has always been /home/myusername/.thunderbird/whatever.default-release, but it wasn't there. Going to Help/Troubleshooting Information/about:profiles shows it there, but won't open it when clicked on. The only place I could find it was in /home/myusername/.var/app/org.mozilla.thunderbird/cache/thunderbird. But when I replaced and renamed the .default-release file there, and then restarted the app, I still did not have my old data. How do I go about this with a flatpak installation? Thanks in advance.