Open the Thunderbird program folder (e.g. C:\Program Files (x86)\Thunderbird) create a new folder named distribution Create a file named policies.json with the following content:   { “policies”: { “DisableAppUpdate”: true } } Thanks to sifferedd.

Revisions: 21 January 2024, first publication The Thunderbird developers are moving to a new user interface code base for Thunderbird 115 and Thunderbird 102 is the last version that will work with the historical userChrome.css customizations. The userbase for Mozilla products has continually shrunk over the past few years and the chances of equivalent customization [...]