I did finally upgrade and now our development version works with RFacebook gem in version 0.9.0. Last weekend I have spent on other tasks, so it took a few days longer.
There is side effect – FFM now works as in_canvas, in_frame and standalone application. How it can be made? First You need configure Your facebook application as in_canvas. Then You set callback_url for some controller (in our case it is CanvasController). This controller role is to render FBML with fb:iframe pointing to Your normal F8 application. Starting from now this application works as iframe version.
Now, if CanvasController will detect with RFacebook in_facebook_canvas? is not in canvas, then should redirect to iframe version directly (with HTTP 302), allowing to run application standalone.
So, when You click on sidebar-nav in Facebook, You will be taken to version embedded into Facebook layout. When You type application address directly in browser, You will get output free from Facebook layout.
At this moment this code is not released to production so I will notice You when You will could check how this looks.