after running TB , in TB if you press [Shift]+[Command]+[B] (in macOS computer) or if you press [Shift]+[Ctrl]+[B] (in WIndows computer) , then TB Address-Book will appear. also see [https://support.mozilla.org/en-US/kb/keyboard-shortcuts this] page, it can detect your OS & shows data based on that. TB main menu > Window > Address-Book. if after some type of auto update or forced update or you selected update , this problem began , then it appears that you were using v68 series TB, & you updated to v78 series TB, and v78 sereis TB , sometime cannot properly convert v68 series Address-Book (mab/mork) files into v78 series (sqlite) files. TB-profile sub-folders are here: "%APPDATA%\Thunderbird\Profiles\<TB-profile-sub-folders>\" that is usually here: "C:\Users\<WindowsUserName>\AppData\Roaming\Thunderbird\Profiles\<TB-profile-sub-folders>\" that "Profiles" folder will very likely have multiple TB-profile sub-folders. go into each of your TB-profile folder: you will find *.mab or *.mab.bak change *.mab.bak into *.mab you may use Converter tools to convert mab/mork into other format CSV,txt,etc files, then you can import into newer TB. another option is to downgrade back to older v68.12.1 TB , export all contacts from Address-book into simple CSV,txt,etc file , then again upgrade to newer TB & import contacts from csv/txt,etc file. 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/1315734#answer-1373022 ATT-Yahoo related settings for TB]. • [https://support.mozilla.org/en-US/questions/1304518 Yahoo related settings for TB]. • [https://support.mozilla.org/en-US/questions/1316618#answer-1374784 Microsoft related settings for 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.

''<p>Zarko [[#question-1320246|said]]</p>'' <blockquote>Please help! I am using Thunderbird for more than 15 years and never had any trouble. Now, suddenly, I cannot access my address book. When I try to get address book, I am asked to give the name of the address book. </blockquote> What do you mean "give the name of the address book"? Please post a screen shot