hi , please see more info on various options here to regain previous data, (though its for Windows, you can understand the pattern then you can apply it on macOS). if you want to, you may see Downgrade option here (macOS). i suggest to disable "auto-update" in TB , link to do that inside above mentioned pages.

There should be no need to downgrade.

Go to help > troublehooting > about:profiles

Hopefully you see two profiles listed. One indicates "This is the profile in use and it cannot be deleted.", which is the profile that is not showing your old mail. You will want to start Thunderbird with the other profile by clicking "set as default profile", then restart Thunderbird.

If you have not correctly installed Thunderbird on the Mac then the process above may not work, and you should consult https://support.mozilla.org/en-US/kb/installing-thunderbird-on-mac

Unfortunately each profile wound up with the same information and none of the old e-mails or contacts. I feel certain my old contacts and e-mails are there but they won't migrate to the new version. Any further help would be GREATLY appreciated. This has been devastating to me and to my business...

For macOS & a second TB:

TB = Thunderbird.

a PLAN : if you downgrade TB into v68 series , & fix address-book , make it simple address book ( do not use any advanced or special or custom types/categories/fields, etc ) , then exit TB & make a backup of TB-profile again , then again try to update/upgrade the old v68 into v78 & see if your address-book problem is fixed or not. below info are detail steps of this paragraph:

( Those who can't view/see the files/folders i mentioned in below, those users can use below commands to UNHIDE the HIDDEN files/folders: • in macOS > start "Finder" app , "Finder" is very similar to Windows-"Explorer" > in Finder. in left side/pane, select "Applications" > then scroll down & go into "Utilities" subfolder > then click on "Terminal" or "Terminal.app" to start it. • type below command inside "Terminal" ( "Terminal" is like Windows "Command-Prompt") : defaults write com.apple.Finder AppleShowAllFiles true • then you must reboot Mac computer OR run this command: /usr/bin/sudo /usr/bin/killall Finder /System/Library/CoreServices/Finder.app then all hidden files+folders will by-default be shown to user in Finder )

( in macOS, inside any file browsing window, user can also press below THREE buttons altogether once, to show HIDDEN files/folders: [Command⌘] + [Shift⇧] + [.^>] if user press-es above three buttons again, file-browsing-window will HIDE the HIDDEN files/folders. )

( By default "Finder" will keep file's extension hidden . We need to see all File's extension . To view all file's extension, do below steps: in macOS > start "Finder" app > goto main menu > Finder > Preferences > Advanced > select "Show All Filename Extensions" option )

• close TB, if its running. • please follow pre-cautionary steps shown in links in my previous post ( you must make one backup/copy of entire "~/Library/Thunderbird/Profiles/" folder, copy that .../Thunderbird/Profiles/ folder into your Desktop. )

• now find out what exact TB-profile sub-folder is used by your TB v78 series: • start this v78 series TB, then goto TB main-menu > Help > Troubleshooting Information > about:profiles > write down the "Root" Directory/folder full PATH (directory PATH structure), what its showing in that line. • we will call it "new-profile" or "new-TB profile".

• exit/close TB.

• lets assume, your username in macOS is "UserName".

• start "Finder" in macOS. • pls create a "MyApps" folder under your home directory here: "/Users/UserName/MyApps/" • then create another sub-folder here: "/Users/UserName/MyApps/Thunderbird-v68/" • also create this folder: "/Users/UserName/MyApps/Thunderbird-Profiles/"

• goto (parent folder of TB-profile subfolders), which is here: "~/Library/Thunderbird/Profiles/" above location is equivalent of this: "/Users/UserName/Library/Thunderbird/Profiles/" • ( inside it will have multiple sub-folders that looks like these: xxxxxxxx.<profile-name> , where x is random alpha-numeric characters/letters/numbers, then <profile-name> may be "default", "default-release", etc, etc ). • write down those folder-names which are not "new-profile" (v78 series TB) folder-name. • whichever folder is not "new-profile", that is your older/earlier TB's profile. • lets call that earlier/older TB's profile : "old-profile" or "old-TB profile".

• copy TB-profile subfolder that is for "old-TB-profile" from under/inside the parent folder ( .../Thunderbird/Profiles/ ) of all TB-profile subfolders, from here: "~/Library/Thunderbird/Profiles/" and paste into this folder: "/Users/UserName/MyApps/Thunderbird-Profiles/"

• please download/get older TB v68.12.1 (download link is inside this page , search for a LINK "Download Thunderbird Installers"). • download DMG file for macOS, for your language. • double-click on the DMG file to open/mount it , a new Volume will appear in "Finder" , it will show internal contents on DMG file, • copy "Thunderbird.app", & paste into below folder location: "/Users/UserName/MyApps/Thunderbird-v68/"

• inside "old-profile" or in "new-profile" , you will find few files that has ".bak" file-extension, find those file & copy them to "old-profile" (if another exist then do not overwrite , just skip ) , then rename them like this: "abook.mab.bak" (this is backup of you old/earlier Address-Book) : rename this .bak file into "abook.mab" file. • ( and find out what other important files there are inside the "profile" folder : goto here & press Ctrl+F to search for "LIST of FILES inside "PROFILE"" )

• open "Terminal" app in macOS, & run any one of these two commands to start (second)-TB, after changing the UserName in the command into your actual username:

"/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app/Contents/MacOS/thunderbird-bin" --allow-downgrade -p "/Users/UserName/MyApps/Thunderbird-Profiles/old-profile"

OR use this command:

/usr/bin/open -n -a "/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app" --args --allow-downgrade -p "/Users/UserName/MyApps/Thunderbird-Profiles/old-profile"

• wait for TB to complete loading/starting up. • first thing you have to do is : disable auto-update . you will find the link (of actual instruction page) here, then press Ctrl+F, & search for "Disable update or auto-update in Thunderbird" , that search will take you into the link . its the 1st link in that page . follow the link , then follow instruction what is useful for you.

• after old TB v68 series starts up, it should show all your previous accounts & data. • but if it does not, then: run (second)-TB with below (any one of the) command (out of two commands), after changing the UserName into your actual username: "/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app/Contents/MacOS/thunderbird-bin" -P --allow-downgrade -p "/Users/UserName/MyApps/Thunderbird-Profiles/old-profile" OR, run with this command: /usr/bin/open -n -a "/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app" --args -P -p "/Users/UserName/MyApps/Thunderbird-Profiles/old-profile"

• a small window will appear from TB, showing you list of available TB-profile(s) , choose "old-profile" or any one which is not "new-profile". • profile choosing window will show only <profile-name> portion , it will not show the alphanumeric "xxxxxxxx" portion of the full profile folder name: "xxxxxxxx.<profile-name>". • so, remember the <profile-name> portion, • in TB, check & find out if the chosen profile in above, is uptodate or not. • if it is not correct, then exit from TB, run previous command again, & try another profile. • when you find the correct TB-profile , remember "profile-name" portion , exit TB , run the above command again & this time choose CORRECT TB PROFILE-NAME, and also choose the "Continue to use this profile as default profile", etc etc option. • after this step you can run TB by using the command without any extra options: "/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app/Contents/MacOS/thunderbird-bin" OR, run with this command: /usr/bin/open -n -a "/Users/UserName/MyApps/Thunderbird-v68/Thunderbird.app"

• now you have working copy of your old-profile & an older version TB.

• you may make address-books simple , (do not use custom fields,etc, instead create multiple entries ) , so that v78 series can convert easily.

• now you decide what to do, upgrade to v78 again or keep using it, etc.

• this is a good opportunity to backup something/data that you wanted to get back.

EXTRA INFO for other/related problems/solutions: • Downgrade TB in macOS: downgrade by using second-TB (this page) , upgrade TB. • Regain old data(in Windows, by using: downgrade process, or second-TB, or manual file-transfer,etc). • Convert mab based Address-Book into other format.