Start Firefox & Thunderbird once and it will create the default folders and profile.ini. Then you can copy your versions into those folders and update profile.ini with your XXXXX.default.
Locations should be as Habitual posted above.
Mine Not sure why I have crash Reports & it looks like my copied one from 2009 as I keep reusing the old one, has slightly wrong permissions, but works. My actual XXX.default is else where in a data partition so I can share it with many installs.:
fred@fred-Precise:~/.thunderbird$ ls -l
drwx------ 3 fred fred 4096 Aug 31 15:19 Crash Reports
-rw-rw-r-- 1 fred fred 94 Apr 18 15:39 profiles1204.ini
-rw-r--r-- 1 fred fred 151 Nov 25 2009 profiles.ini
drwx------ 4 fred fred 4096 Apr 18 15:40 qbugvibk.default