There are choices. - after installing TB, you could exit and invoke password manager and create a profile on D. Then, start TB and add your accounts - or, you could allow the profile to be on C's default, add the accounts, and exit TB and copy accounts (e.g., Imapmail\account or Mail\account to D, then restart TB and on server page, change the location of accounts to point to where you placed them on D. Exit and restart and if all is well, you can then delete the accounts from C to save space. That would leave you with profile on C and accounts on D.

Thanks for the help. What I'm most interested in is not losing any mail. Well, I suppose that's not exactly correct: I won't lose any mail. What I want to try and make sure is that when I start up TB it will "add" any new mail to the existing location on D:. I think there are two things here, no? FIrst, where the profile is stored; and, second, where data is stored. When you use the word "accounts" in your message, should I interpret it to be the same thing I mean when I say "data"?

Yes. To me, accounts refers to the account specifics (e.g., port, server, etc) and the message folders. Thunderbird looks to the profile to tell it where the accounts and folders are.

So, what happened is exactly what I did *not* want to have happen. I added my (existing) gmail account to Thunderbird, and it immediately started downloading mail. All good so far. The problem is that it placed the mail in precisely the *wrong* local folder, which means that I now have "legacy" email sitting in one local folder, and newer mail (as of today) sitting in a different local folder. I can, of course, change the local folder setting in TB - but, and here's what went wrong, only AFTER I start up TB. At that point, it's already downloading messages to the new local folder. If that folder location was in prefs.js before I started TB, I didn't see it.

So, the problem now is: how do I merge the mail from the new folder with the mail in the legacy folder such that all my mail is in a single folder?

Or, perhaps solving the problem differently, any idea how I tell GMail (via a web interface) that the mail should be re-downloaded again after I've changed the local folder setting in prefs.js?

Ok, I've figured out how to tell GMail to let me re-download mail. Looking at prefs.js, though, there seem to be two different local folders referenced (neither of which is the right "legacy" folder, so they're new to this install).

I have:

user_pref("mail.server.server1.directory" set to one folder, and

user_pref("mail.server.server2.directory" set to another folder

I am unsure why these are different, and thus which one to set to the location of the desired "legacy" mail folder.

That "server2" directory seems to have files with zero byte sizes, so that pretty conclusively seems to tell me I need to change the "server1" directory setting, but I'm very curious why there's a "server2" directory shown.