Do you run any technical software, such as Glary or Norton? Such products are known to monitor software updates and to force install in an attempt to provide good customer service. My suggestion is to investigate that angle, as this not a common occurrence. Also, if, from curiosity, you click help>about, the update will be sitting there. So, don't check there. :)

Hi,

As indicated, no updater software whatsoever.

I am wondering if there is something off in my config somehow. For example, there is no app.update.auto preference listed in the config editor. What preferences actually control this in v115+?

R

Thunderbird does not necessarily list any preferences there that are currently set to their default value. In addition to that only non default preferences are saved to disk at all. I doubt that app.update.enabled is even a valid preference these days as updating per se can only be disabled using enterprise tools.

The source is fairly clear.

// If set to true, the Update Service will automatically download updates when
// user can apply updates. This pref is no longer used on Windows, except as the
// default value to migrate to the new location that this data is now stored
// (which is in a file in the update directory). Because of this, this pref
// should no longer be used directly. Instead, getAppUpdateAutoEnabled and
// getAppUpdateAutoEnabled from UpdateUtils.sys.mjs should be used.
#ifndef XP_WIN
 pref("app.update.auto", true);
#endif