We faced some problems between firefox 47 and selenium thats why we decided to downgrade to version 46 on our development and jenkins platforms.
Here simple guide for downgrading it. Sadly ubuntu only support latest version of package (version 47) and version 28 so we will do it manually.
Remove existing one but don’t delete rest:
sudo apt-get remove firefox
get version 46 for 64bit system
wget https://ftp.mozilla.org/pub/firefox/releases/46.0/linux-x86_64/en-US/firefox-46.0.tar.bz2
tar -xjf firefox-46.0.tar.bz2
sudo rm -rf /opt/firefox
sudo mv firefox /opt/firefox46
sudo mv /usr/bin/firefox /usr/bin/firefoxold
sudo ln -s /opt/firefox46/firefox /usr/bin/firefox
Thats all, after these your selenium script can work like before. I tried marionette driver but it doesnt work for me so downgrade was better option.
In case if you installed v46 as package and want to hold its upgrade use this command
sudo apt-mark hold firefox
to unhold firefox package you can use this command
sudo apt-mark unhold firefox
sudo apt-get upgrade
Best Regards