post TB78 the file formats are not compatible.

OPTION-1: • you should use a Portable-Thunderbird (P-TB) for this, more info is shown in option-2 here. • see/follow instructions from that page: (get PortableThunderbirdLegacy v68.12.1 , install it in shown folder, .. ) • create "C:\PortableApps\TB-Profiles\" folder, • then find an old TB-profile inside your TB-Profiles, here (that were using v68.12.1 or older version TB): "%APPDATA%\Thunderbird\Profiles\" • or get an old profile from your backup or other computer. • profile folder looks like "xxxxxxxx.<profile-name>", where <profile-name> may be "default" , "default-release", etc etc. the x in xxxxxxxx is a random alphanumeric char.

• place your old "abook.mab", etc mab files here "C:\PortableApps\TB-Profiles\xxxxxxxx.<old-profile-name>\"

• copy-paste an older TB-profile here: "C:\PortableApps\TB-Profiles\" • then follow the steps shown inside that linked page, to add the profile location into the P-TB in it's "ThunderbirdPortable.ini" file. • start P-TB.

OPTION-2: • read it few times first to understand what this steps are doing, before doing anything: • if you need to obtain v68 old TB, follow the file download link shown here. • you MUST backup your entire "Profiles\" folder: "%APPDATA%\Thunderbird\Profiles\" it usually means: "C:\Users\<WindowsUserName>\AppData\Roaming\Thunderbird\Profiles\" folder. • then, copy an older profile (that was used with a TB that is version v68.12.1 or earlier) into "%APPDATA%\Thunderbird\Profiles\" • remember profile-name, lets call it "old-profile". • place your old "abook.mab", etc mab files here "%APPDATA%\Thunderbird\Profiles\old-profile\" • then uninstall existing v78 TB, • install v68 TB (and do not select the option: "run after installation"), • run below command to force it to use specific TB-profile: "C:\Program Files\Mozilla Thunderbird\thunderbird.exe" -p "%APPDATA%\Thunderbird\Profiles\old-profile\"

TB = Thunderbird.

TB Address-Book files . TB Email files .

TB version , File Name & Extension: • TB v68 series & before uses MORK formatted Address Book ( .mab file ) • TB v78 series & later uses SQLITE formatted address-book ( .sqlite file ) • The "abook.mab" & "history.mab" files are default address books. the "abook.mab" is Personal Address Book, "history.mab" is Collected Addresses. Manually/Custom Added Custom Address Books are: abook-1.mab , abook-2.mab, etc. Imported address book are impab-1.mab , impab-1.mab , etc.

MAB files uses MORK formatted data: • https://wiki.mozilla.org/Mork • https://wiki.mozilla.org/Address_Book • https://stackoverflow.com/questions/17841815/ • https://en.wikipedia.org/wiki/Mork_%28file_format%29 • Mork Syntax , Grammer , Structure.

MORK Converter (into other format): • https://github.com/KevinGoodsell/mork-converter (python . opensource . cost free) • https://metacpan.org/pod/Mozilla::Mork , 2 (perl . opensource . cost free) • https://dxr.mozilla.org/firefox/source/db/morkreader/ (CPP . opensource . cost-free . Mozilla) • demork https://bug241438.bmoattachments.org/attachment.cgi?id=175024 (mork to XML . opensource) • https://www.majorgeeks.com/files/details/dawn.html (email-client address-book files into other format . Not-opensource . cost-free) • https://github.com/qris/thunderbird-ldif (MAB to LDIF . opensource . cost-free)

View Address-Book: • get & load Libre-Office (opensource. cost-free) > File > Wizards > Address Book Data Book Source > Other External Data Source > select a .mab file. ( a driver for opening mab file may-be needed , Libre-Office includes that ) • https://sourceforge.net/projects/mbox-viewer/ (opensource . cost-free).

TB itself can EXPORT into: • LDIF ( *.ldi , *.ldif ) • comma-separated value *.csv • tab-delimited *.tab , *.txt

IMPORT Address-Book: • MoreFunctionsForAddressBook : open Address Book manager from TB > Tools > Address Book . then goto Tools > Actions for addressbook . under it, select "Import addressbook from mab file" . it will ask you to create a new address book by giving it a new name . do so . then, in file navigation window that opens-up , find & goto TB old profile folder location , look for files with .mab extension . select one to import . this way one by one import other address-book (mab) files . when imported address-book items are loaded in TB, you can drag-and-drop addresses from imported books into your new Personal/Collected address book.

Convert SQLite data into CSV format: • https://www.sqlitetutorial.net/sqlite-tutorial/sqlite-export-csv/ • SQLite Management Tools . sqlite data manipulation tool list. • SQLite. • DB4S ^home : DB Browser for SQLite (aka: SQLite Database Browser) . a GUI based tool. • SQLiteStudio ^home GUI based tool for SQLite database browser.

CONVERT EMAILs from mbox file ("mail folder") , INTO .eml files (one message per file , in "maildir") converter: • http://www.broobles.com/imapsize/mbox2eml.php • ImportExportTool addon/extension. • https://download.cnet.com/Mbox2eml/3000-2369_4-75185064.html (Java based tool) • http://www.brothersoft.com/mbox2eml-331429.html (C++ based tool)

CONVERT EMAILs from mbox file INTO XML: • http://tools.elit.nl/mbox2xml.php (cost-free)

References: • http://kb.mozillazine.org/Mail_Utilities • https://support.mozilla.org/en-US/questions/1260419 • http://forums.mozillazine.org/viewtopic.php?f=39&t=1891695

Hi TB Mod/Admin , Please restore my earlier answer/post. after editing the answer , this site showed some error , then the answer/post is not appearing anymore ! please fix, Thanks. -atErik

PART-02 (Address-Book, MORK/MAB, SQLITE, etc)

v68 series TB uses MORK/MAB based files to store TB-Address-Book , and cannot work with SQLITE (used by v78 series TB) based TB Adrs-Book.

v78 series TB uses SQLITE based files to store TB-Address-Book , and cannot work with MORK/MAB (used by v68 series TB) based TB Adrs-Book . But v78 series TB can convert MORK/MAB based files into SQLITE on first time run.

so if you are updating/upgrading from v68 series TB , into v78 series TB , then first EXPORT TB ADDRESS-BOOK into CSV,etc file/format. Later, you can IMPORT that CSV,etc file into v78 series TB Adrs-Book.

if you are downgrading from v78 series TB , into v68 series TB , then also do same as above. or follow downgrade process.

• 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.