I have been seeing questions like this for years, and really I fail to understand what it the problem with a couple of icons on a toolbar. but removing the chat icon is as simple as right clicking the toolbar, selecting customize and dragging the offending icon off the toolbar. My understanding of the calendar is if you have no calendars then the calendar options are mostly invisible or disabled.

Well if you've been seeing it for years - then obviously people don't want the feature and are looking for a way to dump it. BTW in 78 onwards dragging the chat icon off the toolbar doesn't work and nor does disabling the calendar by having no calendars. When you are trying to save space by getting rid of unwanted program extras, and trying to cut the load time, it's very annoying not to be able to do so, in fact it's so annoying I am considering using a different client, and it's obvious I am not alone.

you are imagining that these unused features have any perceptible impact whatsoever - they do not, and they cannot.

Well if you've been seeing it for years - then obviously people don't want the feature and are looking for a way to dump it. BTW in 78 onwards dragging the chat icon off the toolbar doesn't work and nor does disabling the calendar by having no calendars. When you are trying to save space by getting rid of unwanted program extras, and trying to cut the load time, it's very annoying not to be able to do so, in fact it's so annoying I am considering using a different client, and it's obvious I am not alone.

You are not alone in your desire, but I question your motivation as hiding these features offers no benefit towards optimization. All disabling a chat icon does in remove a small image from your screen. The same for the calendars functionality. It is all a part of the main program Changing what you see does nothing at all of save disk space used or optimize the way the program starts up or functions.

Thunderbird stores no settings for "defaults" but it does have to store and read settings for non default setups. These are in all honesty minuscule data reading and storage, but non default settings would technically result in slower execution. A typical setting is something like Feeds.logging.console=Info so you would probably be talking in picoseconds to measure any change. But your efforts to disable these functions will not result in faster execution or reduced storage requirements.

Now one final thing. I am currently using V78 of Thunderbird and dragging the chat icon from the main toolbar removes it from that toolbar. But you have to drop the icon in the customize dialog. This has always been the case, but it is the only thing I can think of that would lead you to think it did not work.