Please make sure "<path-to-profile-folder>\scheduled-notifications\notifications.json" file is not read-only. - - - The following steps might be helpful: 1. Go into profile folder of Thunderbird. You can find instructions on how to go into profile folder of Thunderbird in the following link: Profiles - Where Thunderbird stores your messages and other user data https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data 2. If Thunderbird is open, close Thunderbird. 3. (Inside profile folder of Thunderbird) Go into "scheduled-notifications" folder. 4. (Inside "scheduled-notifications" folder) You will see "notifications.json" file. Make sure this file is not read-only. If this file is read-only, change it to be writable and readable. The following link might be helpful: Change permissions for files, folders, or disks on Mac https://support.apple.com/en-ca/guide/mac-help/mchlp1203/mac 5. Open Thunderbird > "Only 3% of users support Thunderbird" page will show in tab > close the tab > close Thunderbird > open Thunderbird again > now "Only 3% of users support Thunderbird" page should not show at all.

Looks like the latest update solved it. Haven't seen the appeal tab in a couple days.