I\'m on EC2 instance. So there is no GUI.
$pip install selenium
$sudo apt-get install firefox xvfb
Then I do this:
$Xvfb :1
open a terminal and run this command xhost +
. This commands needs to be run every time you restart your machine. If everything works fine may be you can add this to startup commands
Also make sure in your /etc/environment file there is a line
export DISPLAY=:0.0
And then, run your tests to see if your issue is resolved.
All please note the comment from sardathrion below before using this.