Recently installed 18.04, and, as the title explains, I have managed to get GNOME Shell integration extension
to work with Firefox (version 60.0.1) but not with Chromium (version 66.0.3359.139).
I have tried what the link on the GNOME extensions page suggests:
Refer documentation for instructions about installing connector.
and rebooted but that has not solved the problem.
Interestingly enough, before my recent fresh install of 18.04, I was using 17.10 with GNOME and the Chromium integration was working properly.
Some hints on how to debug and fix this would be greatly appreciated.