Why a Host is needed?
As Google Chrome runs in a 'sand box' a native messaging host is need to communicate with Firefox.
The host will run automatically by Firefox each time you will send something to Firefox.
The host doesn't contain any viruses (even if windows defender says so for some of you)!
Just run the installer (No python is needed)
OS X and Linux (Python is needed)
1. Download the rar file.
2. Extract to a folder (do not delete afterwards).
3. Run install_host.sh from the command line.
For those of you that installed the host and it still doesn't work:
1. Install python!
2. Locate the folder of firefox and update it in the options.
3. Restart both Chrome and Firefox and than retry!