Linux kernel is part of many GNU/Linux,etc distro , distro's devs place TB-profile in slightly different locations. usually TB-profile is here: "~/.thunderbird/Profiles/<xxxxxxxx.profile-name>" usually above short-location indicate below folder location: default volume : "/Users/<LinuxUserName>/.thunderbird/Profiles/<xxxxxxxx.profile-name>" the "~" is your HOME directory. some distro may set TB profile here: "~/.mozilla-thunderbird-<xxxxxxxx.profile-name>/" (where x in xxxxxxxx is a random alphanumeric character/letter/number)

let us called computer-S : source / src . (for your case, your ubuntu18) computer-D : destination / dest / dst . (for your case, your ubuntu20)

both must use exact same TB version, during these process . later you can update/upgrade,etc.

in src, goto TB main menu > Help > Troubleshooting Information > about:profiles > Root Directory. write down full PATH shown in root dir line. the last folder in the PATH is the actual TB-profile sub-folder/sub-directory. we will call that TB-profile folder: "src-TB-profile" exit TB.

in dst, goto TB main menu > Help > Troubleshooting Information > about:profiles > Root Directory : last folder in this line is TB-profile sub-fodler. we will call that TB-profile folder: "dst-TB-profile" exit TB.

make a folder called "BAK" in your Desktop. backup/copy all contents inside the "dst-TB-profile" folder , into your Desktop's BAK folder, or where you want to.

copy ALL CONTENTs (files, folders, etc) of "src-TB-profile" folder from src computer , into the dst computer's "dst-TB-profile" folder.

do not delete or change the actual sub-folder-name of : "src-TB-profile" or "dst-TB-profile" , just transfer contents under one, into another.

start dst TB & check if all is working or not.

if mail-accounts in dst TB are asking for password , then close dst TB & you may have to delete the pkcs11.txt file inside "dst-TB-profile" sub-folder once , & restart TB , & re-enter password or mail-key or app-key for your those (all) mail-accounts, bcuz TB sometime cannot load password properly from earlier profile.

More/Related Info: • Disable AV/FW/SS software mail-protection OR enable+add+allow EXCEPTIONS in it & add mail-server names/address . Some AV/SS creates insecure proxy/gateway for scanning/checking emails, but there are other secure way to scan/check emails . Please make sure the option "Allow AV to Quarantine email" is selected inside TB, and make sure your AV/SS is set to Scan all files on access. • Regain old data in Windows : by using downgrade process, or by using a Second-TB, or by using manual file-transfer,etc). • Downgrade TB in macOS : downgrade by using second-TB , upgrade/downgrade TB. • AT&T , ATT-Yahoo related settings for TB. • Yahoo , ATT-Yahoo related settings for TB. • Microsoft Hotmail/Outlook related settings for TB. • Convert MAB/mork or SQLite based Address-Book into other format, mbox email files into other format. • Disabled auto-update or update of TB : inside the linked page , click on the topside 1st link to goto the auto-update disable instruction page into another website.

Hi and thank you for your quick reply, but you seem to describe the move scenario. Have you tried running both TBs at the same time after your procedure, not just the 'dst' machine? And no complaints on either? I did a similar thing as I explained in the initial question, but after checking my same emails on another machine (Win7, I had set up years earlier by hand), I ended up having problems with identities on my mail servers and had to reset, etc (see para (1) above). So pls confirm your practice proves what you recommend, given that I need both or more machines with the same profile data running on their own regardless of whether their cousins are on or off on the other machines with the same profile. And bear in mind that copying all content under, say, a (default) profile folder copies all the file paths/names with that name too; some binary files in there contain that name too when communicating with the mail servers and exchanging passwords. And now imagine two/more separate machines using exactly the same profile data, even the profile folder name, AND sending the same data to the mail servers. It's not for nothing they'll start complaining, is it? So pls confirm you did experiment with your procedure in real life and both/more machine do run their copies of TB with no hindrance. (FYI, there's a shorter way to reach the profile folder via Troubleshooting Information, see pic below)

The link to question that you mentioned may not be the same issues.

Profiles may contain data that described different path directories etc. It would be very different between a Windows OS and Linux OS as discovered in the other situation, but may be identical between (Ubuntu 18) and (Ubuntu 20), so would not present same issue.

It would also be advisable to make sure both computers were running the same version. The version of 68* did have a few different issues that have been fixed in the 78* series.

To provide tech-support to my clients, i have used/copied same TB-profile into/with even nine different computers, at one instance. done these on Windows, macOS, Debian linux, etc. specific settings done in one computer , were needed to be present in all other computers, so i had to copy TB-profile. usually after starting TB, i had to remove earlier mail-account & add corresponding email-account in TB that is right for that specific computer/desk , or, just changed email-address & password in mail-accounts, as all other settings were same. these were done with versions before v68, i don't remember exact version # anymore.

i myself have used same TB-profile with multiple different instance of TB and/or with multiple Portable-TB in same computer, & still do: ( i keep my personal , project(s) , business, etc email mail-accounts separated into different TB ) in macOS, linux, etc it is usually easier to copy content of same TB-profile into multiple different TB & run those TB from multiple different sub-folders . i changed only email-address & password, etc mostly, for my mail-accounts in TB, etc, etc. Portable-TB in Windows also works great with same copy of TB-profile. Portable-TB-for-OSX did not work , ( i could not make it work ) , so instead i used multiple TB from multiple different folder. above are done/tested in pre v68 series , v68 series, v78+ series.

Files inside TB-profile internally uses not-absolute (relative) path when a folder/file is referenced , so moving TB-profile into a different sub-folder does not cause problems.

File system location chars are more same in macOS, linux, unix, etc ... than Windows , so transfer of TB-profile's files in-between Windows and *nix , may cause some incompatibility in some TB versions, and transfer of TB-profile's files in-between *nix (same platforms) , usually has less problems in some TB versions.

But there are techniques to use same (file system) location chars slightly differently, for Windows & in *nix platform software , then that works in both Windows & *nix , etc platforms , So transfer of files,etc from one TB-profile into a different platform's TB-profile can still work fine, and i have noticed, lately, this type of TB-profile (or content of a TB-profile) movement in between different platforms , are not anymore a problem in newer TB versions.

a TB dev can clarify more clearly if TB is actually able to detect+use those platform independent location chars for file/folder location.

internal file format (a file's internal content) is almost same in any platform , specially in newer TB versions.

above are my observations.

EDIT: forget to mention , a shared (SAMBA, NFS, etc) network drive or shared folder(s) in a server computer , is also another way to store multiple TB-profile(s) under multiple shared (password protected) sub-folders for multiple different users . then to share those , in (each) client computer's TB (with different or same platform OS ) : first we need to mount shared network folder with password assigned to the client/user , & change TB's Profile "Root Directory" once in "profiles.ini" file, into the shared TB-profile network location once & set as default TB-profile , ... are what mostly need to be done . How to solve password related issue, etc, etc , if shows up , is shown in my earlier answer.

MozillaZine & TB Support & TB Wiki site/pages have more detail info on these.

Hi, Re: Toad-Hall's comment. Well, it's related, since I hoped to find out the way TB saves pwds deeper than jsoning them against "encryptedPassword" elements in order to no longer need to reenter'em again and again after each profile copy. Still, thank you all. Eventually, back to my ini question, I've resorted to own ways to solve the problem by programmatically copying the src profile data under a newly created profile on the dtn machine, after changing all relevant file content to match the new host folder name vs the src one. This however did not eradicate the need to reenter and remember passwords. Thanks goodness I have up to 7 mail boxes for now. How do I close/archive my question here? Cheers.

once you choose an (any one) answer as a solution , then it will be treated as "solved", and will appear better in search-engines searches, etc.