> dealing with character encoding and supporting the feature is painful (though the will still deal with it under the hood). Mozilla have limited resources and they (and Firefox users) want the browser to be successful and sustainable, and this means focusing resources on things that will make the browser easier to adopt and less confusing rather than chasing the short-lived gains from appeasing a small and stagnant pool of ‘power users’.

Dealing with character encodings is indeed painful, but they are not dropping support for all of these legacy encodings. If they did, I am sure it would simplify things a lot in terms of maintenance, but they are too widespread in existing content to do that. Firefox will still use a legacy encoding if it detects it. All they are doing is removing the ability to tell Firefox that a website uses a certain encoding. The idea that this option is a maintenance burden is kind of hard for me to believe.