I have a fairly complex IMAP tree with lots of folders and sub-folders. Thunderbird periodically resets the sorting of messages to earliest message first, and now also "threaded" view has become some sort of default. I have to go through each folder and reset the sorting the way I want it, which is a painful process.
It should be possible to set sorting of messages as a global function. And not have Thunderbird arbitrarily reset them later, but at least give the user the option of setting them how they want, easily.