They should be located under the "Extensions" icon (by your search bar, next to the "hamburger" icon (i.e., most right icon)). It looks like a puzzle piece.

Regardless, this is not a Kali issue, and I cannot replicate your problem on a freshly installed Kali Linux XFCE.

Hi Arszilla,
yes, this feedback did help. Although the extension symbol did show all plugins, I first could not find a button for the settings during browsing (what I mean is an option to allow or disallow URLs in noscript). I only found
activation and deactivation.

However, in the extension tab, there was the option for all plugins, to stick them to the menubar, which I did. This option is NOT available in the settings menu of firefox, when you go to "plugins and themes".

So, it was like I thought: not a bug, just a special setting in the version of firefox in kali and so I allowed me, to ask here.

Thius issue can safely be closed. Thank you for the fast and helpfull response.

Best regards

Hans

Again: This is not a Kali specific issue. This change was introduced by Mozilla a few months back and its multi-platform. I have observed it on Windows and Linux.