Rated 5 out of 5 stars
This is main reason I'm running firefox. I love this app, and just counted to 18462 .maff files on my laptop.
Of course it is totally unacceptable with software changes which makes such an essential add-on incompatible.
However, I'll continue to run firefox 56 as long as I'm here and haven't got another browser to work with the tremendously fantastic maff format. The so called MHTML or MHT is simply not an alternative. I don't like it, and there are no tools for handling it (only count free open source tools).
So from firefox version 57 firefox is dead as long as MAFF format is not supported.