1. Very few people use this feature but a few vocal users who are particularly good at navigating bugtracking bureaucracy do use it and care deeply.
2. Of all Firefox users, a small percentage speak languages for which there are many non-ascii letters and a relatively large amount of pre-Unicode content online, and of those users a small percentage read niche (eg non-facebook and old) sites with broken character encoding.
Both situations could probably lead to few uses of the menu in telemetry. Perhaps we should care more about users in the second category as they are perhaps more correlated with other things like location whereas the first set may be more uniformly distributed across the population. I think other points are also being disregarded:
- ordinary users may find the feature cryptic and confusing. Or at least undiscoverable
- 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’.