Hi jimfrancis, the Firefox logo is not the Firefox button, but you should be able to get the Firefox button by right-clicking in an empty space in one of the bars at the top of the browser and clicking 'Menu Bar'. The Firefox button is not essential however, as the File, Edit, View... menus provide the same functionality (but some help articles might only give instructions involving the Firefox button).

I'm not sure what you mean by a menu button, but you can add/remove buttons and move them around by right-clicking in an empty space in one of the bars at the top of the browser and selecting 'Customize'. You can then drag and drop icons/buttons from the window that appears up to the bars at the top of the browser to add them. You can also rearrange the buttons by dragging and dropping them to other places on the top bars and you can remove buttons by dragging them from one of the top bars to the 'Customize Toolbars' window.

When you are on the about:addons page then most of the toolbars will be hidden and you may only see the Tab bar and not the Firefox menu button. I'm on Linux and there the Firefox menu button is on the Tab bar and still present. Note that if tabs are not on top (browser.tabs.onTop = false) then you see all toolbars when you open the about:newtab page, but this won't be possible anymore in next Firefox versions with the Australis interface.