GNOME shell extension doesn't work with snap version of web-browser

Got an error from Firefox saying :

Although the GNOME Shell integration extension is active, the native host connector is not recognized. Please consult the installation manual.

Which is an error that seems to never happen, I'm using Ubuntu 18.04 (Dual Boot Windows 10), and yes GNOME shell is installed via

sudo apt-get install chrome-gnome-shell

I'm using Firefox v64.0.2 (64 bits) snap.

Could someone help?

Since you're using the snap version of Firefox 64.0.2, it's not unexpected given various restrictions of snappy.

This issue is already raised in snapcraft forum: https://forum.snapcraft.io/t/firefox-snap-is-unable-to-access-chrome-gnome-shell-connector/4562, but unfortunately no solutions were provided there.

Similar issue can be seen with the Chromium snap too: https://forum.snapcraft.io/t/chrome-gnome-shell-does-not-work-with-chromium-snap/3377/2
(see the bug-report)

You don't need to install extensions from extensions.gnome.org as they are also available in 'Ubuntu Software' app.

Launch Ubuntu Software, click add-ons, click extensions tab. Here you are able to install extensions.