Its great, I am using it now, but as M_e correctly pointed out, this is only the preview release. We have a couple of Release Candidates (RC) to come before we hit 1.0 final.
When it does come out, I don't think Mozilla will release it quietly
And indeed this is still far from any final release. This is supposed to be 0.10, commercially they preferred to label it 1.0PR, although it has a couple of major UI flaws that will have to be fixed before.