Telemetry data indicates that Kazakh is the locale where it is the second most common for the user to invoke the character encoding override: https://bug906032.bugzilla.mozilla.org/attachment.cgi?id=796536 Having to invoke the override is bad for the user experience. It turns out that the Kazakh locale sets the fallback encoding to UTF-8 even though the dominant legacy encoding for Cyrillic content in the region is windows-1251. Please change the fallback encoding (intl.charset.default) to windows-1251. For more information about why it is a bad idea to set the fallback encoding to UTF-8, please see https://developer.mozilla.org/en-US/docs/Localizations_and_character_encodings

[fixed by bug 910192]