Hello Watford,
Getting the "du" report to list all directories may sometimes leads to confusion/misunderstanding, especially if you fed the results thru a "sort -nr" filter (which is what I suspect you did).
To get the clearest picture of usage by Thunderbird, you need the results from these two commands:
du -sh ~/.thunderbird
du -sh ~/snap/thunderbird
Those would give you the results identified by @ricmarques , being
141G /home/user/.thunderbird
189G /home/user/snap/thunderbird
Having said that, all the content of the first one is your personal data: setup data, email, GUI preferences and add-ons.
As for the snap package installation, only the portion under "~/snap/thunderbird/common/.thunderbird" is that same personal data, even though it seems to have bloated up.
To me, that is a sign that either
-
you have downloaded an extra 48G of email content (obviously not likely) or
-
Thunderbird has changed it software architecture in such a fashion as to "bloat".
That is exactly what should be expected from Thunderbird to conform to Snap expectations of being fully independent of OS libraries to operate.
As for the 1G difference between these two,
189G /home/user/snap/thunderbird/common
188G /home/user/snap/thunderbird/common/.thunderbird
that is the Thunderbird software itself, again bloated to be OS-independent, as far as is possible, to conform to the Snap dictates.
IF your intent is to keep the SNAP-based Thunderbird installation, then make a frozen backup/offline image of the contents of ~/.thunderbird , then purge that entire directory.
On the other hand, IF your intent is to stay with a non-SNAP Thunderbird
AND
IF you haven't downloaded any email since before your Snap install, then everything under that SNAP Thunderbird is "throwaway".
Just make a backup of your ~/.thunderbird before cleaning up the Thunderbird install as non-snap.
One last observation.
You have directories
ImapMail/imap.gmail.com
ImapMail/imap.gmail-1.com
That tells me that, under the old non-snap Thunderbird,
-
you may have created a second email profile for Gmail in your Thunderbird, or
-
you did some kind of restore/repair of your old email account at some point but did not finish with the cleanup.
If you check which of those two,"imap.gmail.com" or "imap.gmail-1.com" is the path being pointed to by your Thunderbird client by checking
you can then decide which is your "master" email account and which is your "old" or "defunct" ... or possibly "alternate personality" for accessing GMail.
If not that last one, then the non-master account is OLD and can simply be purged, as long as you are sure that you reclaimed all email from that during your previous recovery attempt.
If you need to review the contents of that older account, I will lets someone else guide you thru the steps of setting that up to perform that in a way to allow you to move files from one account to the other.
If none of the above applies to your case, let me know and I will purge my reply to avoid confusing others. 