Rated 4 out of 5 stars
It's working with FF5 now, but he Sync is broken. :-(
Maybe support XMarks? The internal Sync of FF sucks!
I had a look in the issue, but synchronisation works fine for me in FF5. Please try again and send me an email to email@example.com.
Regarding XMarks: At least in foreseeable future, there will be no integration with this service. FloatNotes just stores the data differently and I don't have to time to make major changes to the plugin. I know that FF Sync has issues but I hope it will get better with every version.