Ubuntu – Cannot start firefox on X11 forwarding SSH session

I have installed Ubuntu Desktop 16.04.2 LTS and want to start firefox from my X11 forwarding ssh session but I get the following error message:

user@user-Virtual-Machine:~$ firefox
Failed to connect to Mir: Failed to connect to server socket: No such file or directory
Unable to init server: Broadway display type not supported: localhost:10.0
Error: cannot open display: localhost:10.0

I am using the latest version of BitVise SSH Client

The settings in my SSH client look like this:
click here for X11 client settings

My sshd_config looks like this:

Port 22
Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
UsePrivilegeSeparation yes
KeyRegenerationInterval 3600
ServerKeyBits 1024
SyslogFacility AUTH
LogLevel INFO
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server

What am I doing wrong?