The addon was abandoned by its author because Mozilla was making major changes to the addon API at the time. Extensions used to have carte blanche to change the browser, which was a security risk, not to mention it made threading/parallelizing the browser hard. The new extension API removed a lot of that freedom. After the API change, it wasn't possible (and might still not be) to develop a useful tab groups addon with the new API, so the author ceased development.
I can't imagine Mozilla crippling the addon API to the point where it can't grab data off an RSS feed and display it.