For those wondering why Mozilla wants to deprecate HTTP, the reasons are spelled out above. As Kerry said
Concerns of spying by governments and commercial entities is increasing constantly, and HTTPS may become the norm very soon.
In other words, those with power to spy want to spy on on those without. HTTPS can make spying on raw internet data much harder. It's not a complete solution by any means (it has no effect on websites selling data, and probably won't affect tracking cookies), but it is a good step forward.