You have it in FF for android.
Rendering engine is ready too.
But its addons, and other stuff that need polishing! There are people who complain about separating pugins into separate processes. Wrong multi-process implementation will be 10 times worse.
Also Mozilla is working on dev tools for webmasters adjusted to new FF.
In other words:
You have to wait to get it right.
In the mean time enjoy Azure, smaller memory footprint, etc.