Did you test it as an add on or did you check out the source code?

After you install the extension you can just open it by clicking on the icon to open the chat in the side bar.

If it's the source code, you should be able to just do
`npm install`

and then

`npm start`

This will automatically open the extension in the browser but only for the `localhost` URL 

 so npm install does the same thing as adding browser extn ?
what u mean by can be used in any website ? 
Firefox after install popup opens - if closed it cannot be opened any more 

 The node package manager (npm) is just to install the dependencies. You could build the code for the extension on your machine and load it manually into Firefox.
Or you just install the extension. The addon store of mozilla checks the code too. Depends on your trust model:)

In any case, the sidebar does not open again even after clicking on the icon?