Hy, installing firefox 50 on the computer at work i see that firebug is in built-in but sincerely i don't like this version of firebug, i can't find a console window to write javascript code, i see that there is only one line to write javascript code and test it in run time on the browser, this is not good, like programmers we always test javscript code in console windows so we need a console like as the old one not just one line to write code.
For the moment i use firefox 49 and firebug 2.17 untill all will be fixed and confortable, like programmers we must have quickly under eyes post and get php calls and javascript code, and a javascript console confortable not only one line to write code.
Ciao
Andrea