So if you think it is time to get rid of the old Firefox, the first thing to do is to make sure that it is set as your default browser. Of course, we assume you have installed it already

So, in terminal just type:

sudo update-alternatives --config x-www-browser

(I have found an alternative spelling for config with a single slash '-' which does not work for me )

Then just choose the number for /usr/bin/google-chrome, in my case it is 4.

The good part is that this default setting works not only with Gnome but also LXDE as in my case.