Under 'Application Basics' - Profile Folder - click on 'Open Folder' 

   Exit Thunderbird now - this is important. 

   cert8.db - obselete file
   cert9.db - currently used file
   key3.db - obselete file
   key4.db - current used file
   logins.json - current used file
   pkcs11.txt (some people report this file missing)
   secmod.db - obselete file
   session.json
   xulstore.json 

   Top 10 Contributor

I Menu app icon > Help > More Troubleshooting Information Under 'Application Basics' - Profile Folder - click on 'Open Folder' This opens a new window showing the contents of your current in use profile name folder. Exit Thunderbird now - this is important. Look for the following files and delete them. cert8.db - obselete file cert9.db - currently used file key3.db - obselete file key4.db - current used file logins.json - current used file pkcs11.txt (some people report this file missing) secmod.db - obselete file session.json xulstore.json See next comment before you start Thunderbird as you need to empty cache files. Start Thunderbird Add yahoo and make sure all the settings are correct. Make sure Authentication Method is Oauth and user name is full yahoo email address. Report on results. Modified 15 zuwɛn 2022 23:27:52 -0700 by Toad-Hall Toad-Hall Toad-Hall Top 10 Contributor 15/6/2022 23:26 Chosen Solution ADDITIONAL Whilst Thunderbird is closed - after you have deleted the files mentioned previously. access : C:/Users/ User Account/Appdata/Local/Thunderbird/Profiles/ Please note this is the Appdata 'Local' location which the computer uses as a cache. Be sure you are in the 'Local' and not the 'Roaming' Delete the contents of the 'Profiles' folder. then start Thunderbird. keep having to reset my secure key password and tried this in "Roaming" instead of "Local" Help!