console.log() doesn't work anymore in Firebug since Firefox 51.0.1
I've just updated firefox to a Firefox 51.0.1 (32-bit), and after the update console.log stopped working.
When I am tring to test some JavaScript variables using console.log(), it doesn't output anything.
Answer
As I mentioned in another answer, this happens because the Firefox internal APIs, which Firebug uses to output the data, have changed. When you open the Browser Console, you'll see the following error:
TypeError: ConsoleAPIListener is not a constructor console.js:149:38
Note that, as stated in a thread in the Firebug discussion group and on the Firebug homepage, Firebug is discontinued and unmaintained. I.e. it breaks more and more with every new version of Firefox and will quit working completely once multi-process Firefox is enabled. There is a blog post explaining the reasons.
The team behind Firebug advises to use the Firefox DevTools instead and there is a migration guide available.