It really pisses me off that even Firefox on desktop tries to scare you away from about:config with a lie, claiming that using it will void your warranty. Meanwhile the license under which Firefox is provided says "Covered Software is provided under this License on an "as is" basis, without warranty of any kind"

Firefox has no warranty to void. The warning message they make you view the first time you try to use about:config is simply lying to you. You might say "Oh well it's a well intentioned lie", but it's still a lie and there is no reason for this lie to even exist. The warning could be worded without this lie. It could simply say "You might break stuff if you continue" and that would be true enough and still scare off people who don't know what they're doing. So why the hell are they lying?