going back to previous version is "downgrade" / "rollback". please see (unofficial) info in linked pages. More/Related Info: • [https://support.mozilla.org/en-US/questions/1315734#answer-1373915 Disable AV/FW/SS software] mail-protection OR enable+add+allow EXCEPTIONS in it & add mail-server names/address . Some AV/SS creates insecure proxy/gateway for scanning/checking emails, but there are other secure way to scan/check emails . Please make sure the option "Allow AV to Quarantine email" is selected inside TB, and make sure your AV/SS is set to Scan all files on access. • [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 AT&T , ATT-Yahoo related settings for TB]. • [https://support.mozilla.org/en-US/questions/1304518 Yahoo , ATT-Yahoo related settings for TB]. • [https://support.mozilla.org/en-US/questions/1316618#answer-1374784 Microsoft Hotmail/Outlook related settings for TB]. • [https://support.mozilla.org/en-US/questions/1317619#answer-1375337 Convert MAB/mork or SQLite based Address-Book into other format], mbox email files into other format. • [https://support.mozilla.org/en-US/questions/1316147#answer-1372552 Disabled auto-update or update of TB] : inside the linked page , click on the topside 1st link to goto the auto-update disable instruction page into another website.

> not very user friendly What about it is not user friendly?