All, As part of https://bugzilla.mozilla.org/show_bug.cgi?id=1772023 I tested with Thunderbird 102 Beta. There are a number of changes between 91 and 102 (for the good, new address book format -- no more Mork!, etc.) that will make irreversible changes to your thunderbird profile. If you are considering "checking out" a new version of tbird, make a backup of your current profile before trying the new version (thunderbird wisely creates a new profile, but for testing CPU use, I needed to use the same account setup). The downside of the new profile creation is if you have a number of mail and calendar accounts to integrate, creating a new profile from scratch will be tedious and the sync of all mail headers, indexing, etc.. can be extensive if you have a large mail-store. So after backup, you can point thunderbird to your existing profile with the '-profile /path/to/your/profile' option and it will use and convert your existing profile to the new format. (but without a back, you will be unable to use the old version of thunderbird with that profile) The good new is High CPU use is gone in 102 beta... -- David C. Rankin, J.D.,P.E.