I rely on Firebug as a Firefox add-in and was seriously dismayed when I installed Firefox 50 to find that Firebug had stopped working. I believe that this is because from version 50 Firefox is multi-process.
Anyway I found a little work-around that gets Firebug working again. Install Firequery after you upgrade to Firefox 50 and Firebug will start working again. Simple!
http://firequery.binaryage.com/
