I had the issue of the missing icons as well, but there’s a user style sheet that fixes the problem (so you can see the cog to access the quiz setting). I also struggled with this when I installed in March. It feels so long ago.
This was the thread that gave me the advice I needed. [With thanks to again to prouleau and others.]
For me the issue was I hadn’t installed the Stylus extension, so the style sheet that made the cog and other features visible wasn’t being included.
This is what it should look like with the settings cog visible, just under the close-window x in the top right.