It simply does not work anymore, even before FF 57: I have set the default to 80%, new sites always show up at 100% and sometimes even 120%, never 80%. And in any case, when FF is rebooted, everything has to be done again.
How come that such an extension, which is pushed by Mozilla itself (how come the function is not a FF built-in one?) has become that erratic in the past weeks?
What are the alternative tools?