I'm trying to use install an extension from https://extensions.gnome.org/ using Firefox 51 on 16.04. I followed the instructions and installed the Gnome Shell Integration as well as chrome-gnome-shell. However, when opening https://extensions.gnome.org/ I still get a hint to install the above:
Follow this instruction and post output here.
If you are getting "shell_version.unpack(), Exception: 'NoneType' object has no attribute 'unpack'" error, then you are not using GNOME Shell.
Obviously GNOME Shell extension and GNOME Shell integration works only with GNOME Shell.