Not very robust Rated 3 out of 5 stars
This doesn't appear to add any offline browsing capability to FFx. It appears to be a simple shortcut and indicator. As such, it works fine.
I was hoping it would add the ability to browse from cache. It doesn't appear to do this any more than the native (File>Work Offline) method.
Also, like another review stated, it should have the ability to be persistent between browser sessions (implemented as an option/preference).