I need to get the native host connector working with Snap version of latest Firefox on Ubuntu 18.04 so that I can install Gnome extensions from extensions.gnome.org.
As it is now, I get the error
Although GNOME Shell integration extension is running, native host connector is not detected. Refer documentation for instructions about installing connector.
Native host connector works with Firefox when installed via apt.
You don't need to install GNOME extensions from extensions.gnome.org. In 18.04 and later it's more convenient to install GNOME extensions directly from Ubuntu Software.
In Ubuntu 18.04 and later GNOME Shell Extensions can be installed from the Ubuntu Software app. Do a keyword search for "GNOME shell extensions" and the type of app you are searching for.
You can also search from all of the available GNOME Shell Extensions on the same screen by pressing Add-ons button which is located under the Categories heading. In the Add-ons screen select the Shell Extensions tab and you will see all the available GNOME Shell Extensions.
Clicking on a GNOME Shell Extension in the list of search results will bring up its screen which will often show screenshot(s).
Clicking on the Website button will open its website in a web browser where you can view a larger sized image of the same screenshot that was shown in Ubuntu Software.
Clicking on the Install button will install the extension.