See http://www.radialthinking.de/radialcontext/ for the original version. This one should offer everything that version has, uses some new Firefox features (mainly the preference system) and contains various bugfixes (menu works on xhtml pages like Firefox error pages, should be less likely to get "stuck", probably more I forgot) and feature additions (customizable menu, more flexible tooltip settings, hopefully better interaction with pages trying to disable the right mouse button).
It should look and feel very similar on the surface, but I have made a lot of changes under the hood (which is why I did not submit this as a patch to radialcontext or radialcontext-D). Feedback and bug reports are greatly appreciated.
Please skim the "about" tab in the preferences dialog for more information.