Ubuntu 17.10: problems with gnome extensions

After migrating to ubuntu 17.10 the unity desktop is gone and the system starts up with gnome 3.
As i wrote here, there are some problems with window decorations which can be fixed by (re-)moving some directories.

But i still had some problems with gnome extensions (screenshot gnome-tweak-tool):

The installation process via the webpage gnome extensions worked fine, but e.g. the system monitor did not show up...

The solution was easy:

apt install vanilla-gnome-desktop

And after this fix the system monitor is there: