The Firefox snap is unable to install extensions off http://extensions.gnome.org as it it can’t detect the presence of chrome gnome shell connector though the package is installed and works perfectly with the deb version. I had earlier reported the same issue with the Chromium snap. Chrome Gnome Shell does not work with Chromium snap
Prashant L Rao
This is failing even earlier for me: when installing the browser extension, I get the following error message:
GNOME Shell integration could not be installed because it is not compatible with Firefox 59.0.1.
And note that for the chromium snap the issue is tracked by bug #1741074. It is likely the same root cause for the firefox snap.
I asked this same question on askubuntu.com. No replies there either yet. Just linking the two up.