Chrome has been pushing the same thing (deprecating plain-text HTTP and/or visually marking it as non-secure) for quite some time, and they've been very clear t

Chrome has been pushing the same thing (deprecating plain-text HTTP and/or visually marking it as non-secure) for quite some time, and they've been very clear that "localhost" will still be considered a secure origin. I don't see any reason to think that Firefox would behave differently.