Looks like we got a little off topic here
What Denys said does work. But you need to do a few things first.
1) Make all hidden files readable.
http://www.mactricksandtips.com/2008/04/show-hidden-files.html
2) Use finder to copy the Thunderbird folder onto your desktop. You can find the folder here: /Users/"YOUR USER NAME"/Library.
""Denys_B
I found I could transfer emails from Thunderbird on the Mac to Mac Mail as follows.
1. In Mail, use Import... Choose from Thunderbird (obviously)
2. In the dialog select the folder Library/Thunderbird/Profiles in your home folder. Mail will then come back with a list of files which it proposes to import. (I left them all checked, even the Trash, Spam etc)
3. Mail creates a folder On My Mac called Import containing the file, and confirms this.
4. Go down the directory tree until you find the emails you want to transfer. In principle you can now select them and drag them to e.g. your Inbox and Sent folders. In practice, I found that it was better to transfer no more than 500 emails at a time, because the process is quite slow without necessarily indicating when it is complete, so it looks as if only some of your emails have successfully transferred. Interrupting the process seemed to lose emails in transit. So...
5. Create some new Mailboxes On My Mac reflecting the mailbox structure you want.
6. Select the emails you want to move and drag them (no more than 500 at a time) into your newly created Mailboxes, or the Inbox and Sent trays. Wait for the transfer to complete!
7. Once you have transferred them all, select the Import folder and delete it.
Downside of all this is that all the emails come across as Unread, so you don't know which ones you have replied to.""
Importing all your mailboxes at one time will take a long long time and MAIL will probably hang or crash if it comes across some corrupted data. I suggest importing 25 or less boxes at a time especially ones with emails containing large attachments. You can monitor the disk activity with activity monitor during the process to see if it has hung. Hint - click on the small dot above the check marked boxes to uncheck them all.
Select all all your new mail boxes, right click or control click, select mark all as read.
I imported about 100 local folders and mail box settings this way and now have all my saved emails in MAC Mail. I too started from Linux using Thunderbird. But after being attack by a malicious web sight and having to restore my Mac mini from the time machine backups, I have decided to remove all programs that use a windows emulation software and all the windows emulation software like WIne, WIn32 etc. I was running Parallels which I now know is a BAD idea. I am waiting for Apple to abandon in Intel processor in favor of the ARM processor like the iPhone and iPad. This will eliminate any windows viruses infecting our MAC's, just like the old days.