WebRender is coming but absolutely isn’t ready yet; it’s not even turned on by default in Nightly (although I use it on my home machine and it’s getting a very good very quickly).

And there is no integrated Firebug - just replacement.

> The good news is that all the capabilities of Firebug are now present in current Firefox Developer Tools.

> Firebug 3 ... was built as an extension to built-in Firefox devtools and eventually integrated directly into devtools.