silverman166, did you get your problem sorted out?

if the mab/mork based TB Address-Book has any complex/custom fields/categories,etc then v78 series TB cannot convert it into sqlite format successfully , but with newer versions its becoming better in that conversion process, i guess. see if any tools from here is useful or not: [https://support.mozilla.org/en-US/questions/1317619#answer-1375337 Convert mab based Address-Book into other format]. if that does not help or you cannot do/apply any. then i suggest to downgrade to previous verison TB first & use older TB-profile , then manually convert the Address-Book into simpler addess-book , or EXPORT into CSV,txt,etc file, which you can later import into v78 series. please see below linked pages+info, try to understand steps, & apply what is useful for your case. INFO for related/other problems/solutions: • [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. • [https://support.mozilla.org/en-US/questions/1316147#answer-1372552 Regain old data](in Windows, by using: downgrade process, or second-TB, or 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 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].