The new about:config interface shows the context menu for nomal pages which is 99% useless with elements like: select all, back/forward/refresh/bookmark buttons, save page, page data, page source, when nothing is selected. Ant the context menu for selected text (or url) when something is selected.

But useful items from the old one are missing. Can't copy the setting's name, value, or create a new one, or reset.

I can see two separate issues mentioned here. For "about:config" specifically, it is intentional that the operations that were previously accessible through a XUL context menu are now delegated to visible buttons and to standard HTML selection and copy-paste functionality.

The presence of useless items in the context menu is a different issue, and it affects every privileged in-content page based on HTML, like about:preferences, about:logins, and so on. I don't think this is necessarily a problem, but if you'd like a second opinion I would recommend filing a bug in the "Firefox :: Menus" component, if one doesn't already exist.