Firefox's literal only advantage over Chrome is its extensibility, and that baby is being thrown out with the XUL bathwater. It's slower than Chrome, it's less secure than Chrome, and since Mozilla seems hellbent on turning Firefox into Chrome, I might as well just bite the bullet, use Chrome and save myself the headache.
The only other advantages I can see are philosophical, rather than practical, but given their history of shoving irrelevant shit into the default install and ignoring any and all user pushback to their decisions (the "we're forcing addon signing" comment section was unanimously negative), I'm not sure that's worth much either. If I want to use a browser where my input on features and so forth is discarded, again, I might as well use Chrome and gain some speed and security while I'm at it.
I ask this question in complete sincerity: Why would I want to use Firefox?