Just follow the steps from the link. I removed the star and was able to put it back in that version of Firefox.

    Click the Page Actions menu button (•••) to open the menu
   Right-click "Bookmark This Page"
   Click "Add to Address Bar"
   Click the Page Actions menu button to close the menu 

Is there a reason for the old version?

Just follow the steps from the link. I removed the star and was able to put it back in that version of Firefox.

If the linked answer would have solved my problem, than I would not have opened a new question. Did you check my screenshot ?

Is there a reason for the old version?

As I told, I am using debian bullseye, that's already the "testing" branch. Stable uses even older ff. I am not interested in compiling ff from source.

Ok... following the instructions from the link you provided... see screenshots

You need to left-click the three-dot icon to open the page actions menu. In the drop down menu you need to right-click the line with the star (Bookmark This Page or Edit This Bookmark) and via this context menu you can add this button to the toolbar. From your screenshot it looks that you left-clicked "Bookmark This Page".

Ok, right click, not left finally found it, thanks !

May I mention that this is bad UI design ? People dont expect to be able to right-click inside a menu. Most GUI software does not support that.

I would rather expect such an option via right-click on "..." --> configure. /Currently right click on "..." does nothing.

(Looking at other related support requests, it seems like I am not the only one which needed to ask the support to find the option)