I'm not sure what you mean by scope - but I will assume you mean functionality. In case you meant something else, do let me know.
The Firefox version lags behind the chrome version because it took a long while for the Firefox add-on to get approved. The Firefox add-on is currently at version 1.4 while the Chrome extension is at version 1.5. The new scrolling feature and google indexation information will not be found in the current version of FF add-on. However, we are adding that functionality to it right now and so hopefully should have an FF add-on update soon.
Going ahead we will try and keep both the chrome and FF add-ons on the same current version. But we will build functionality for the chrome extension first and later port it to Firefox since the chrome publishing process is much more faster.