TB-profile in Linux (ubuntu,etc) can be in slightly different folders, but general location is here: "~/.thunderbird/" or here: "~/.mozilla-thunderbird-<profile-name>/" the "~" aka $HOME directory is usally here: "/Users/<LinuxUserName>/" so mentioned TB-profile is actually here: "/Users/<LinuxUserName>/.thunderbird/" you will find TB-profile sub-folders "xxxxxxxx.profile-name" either under above mentioned two location, or under "Profiles" sub-folder. try to use exact same version of TB what you were using earlier. if you find "*''.''mab''.''bak" files inside TB-profile folder, rename them back to "*''.''mab". files/folders that uses dot "." as 1st char/symbol, are hidden files/folders , so in your File-Browser software : select the option to Unide them 1st or Show hidden files. if you press Ctrl+H in file-browser , then hidden files will be shown , another press of Ctrl+H will toggle the view mode & hide them. disable auto-update in TB. once/when mail-accounts, settings, etc are working fine, then export Contacts from TB-Address-Book into CSV,txt, etc file. update/upgrade TB into latest series/version of TB. import contacts from CSV/txt,etc file. see macOS & windows based info pages linked in below, then you can apply similar pattern in linux. More/Related Info: • [https://support.mozilla.org/en-US/questions/1316147#answer-1372552 Regain old data] , in Windows : by using downgrade process, or by using a Second-TB, or by using manual file-transfer,etc). • [https://support.mozilla.org/en-US/questions/1304550#answer-1352743 Downgrade TB] in macOS: [https://support.mozilla.org/en-US/questions/1317224#answer-1374579 downgrade by using second-TB] , [https://support.mozilla.org/en-US/questions/1318142#answer-1377801 upgrade/downgrade TB]. • [https://support.mozilla.org/en-US/questions/1317619#answer-1375337 Convert MAB/mork based Address-Book into other format]. • [https://support.mozilla.org/en-US/questions/1316147#answer-1372552 Disabled auto-update of TB] : inside the linked page , click on the topside 1st link to goto the auto-update disable instruction page into another website.