fishingfool said:
You're welcome.

To hide the puzzle piece:
about:config => extensions.unifiedExtensions.enabled = false. Restart firefox\waterfox.
So far it hasn't re-appeared in any update
I tried this and it doesn't work for me on Waterfox G6.0.8. On the older versions this puzzle did not exist on Waterfox so I don't know.
This extensions.unifiedExtensions.enabled even when you manually add doesn't seem to have an effect. It looks like it has no effect on Waterfox (at least this latest version).

The only thing that is working is this line in userChrome.css
#PanelUI-menu-button {display: none;}

#unified-extensions-button {
display: none !important;
}

#alltabs-button {
display: none !important;
}

But like I said the the extensions remain hidden and cannot be taken out until I undo the change so the puzzle returns.