"dark under the stars when it was fearless"?
 

The bold is mine. This part of the text has puzzled me for many years. Can anyone tell me, exactly when was the dark under the stars fearless? Did not Morgoth enter Arda as soon as it was made?

before the Lamps?

Speculation...
 

Perhaps before Morgoth sent forth his hatred and malice and polluted the darkness into something that came to be feared?

Ugh. I don't actually own a copy of the Silm ( :( *sniff, sniff* ; I get it from the library), so I can't look this up, but doesn't it say something about the darkness growing evil after Orome finds the Eldar ?

According to the Sil, when the Valar first created Arda and lived in it, "The First War began before Arda was full-shaped, and ere yet there was anything that grew or walked upon earth; and for long Melkor had the upper hand."
Subsequently Arda was lit by the Lamps of Aule and Yavanna. Then Melkor destroyed the lamps and marred Arda, and the Valar withdrew to Valinor. "But as the ages drew on to the hour appointed by Iluvatar for the coming of the Firstborn, Middle-Earth lay in a twilight beneath the stars that Varda had wrought....and in the darkness Melkor dwelt, and still often walked abroad, in many shapes of power and fear..."

Perhasp, since Melkor HQ was way up North, Bombadil's gigantic forest was spared from his evil, and so it seemed safe? And then when he returend to Middle-earth it was as if he'd really, truely, made his presence known in that part fo the world for the first time?

Maybe. But it's funny, he talks about the first acorn and the first raindrop, but the other events he refers are mostly fairly recent in the scheme of things, from the end of the First Age onwards. And the Dark Lord he refers to, was it Morgoth or Sauron? The hobbits would naturally assume Sauron, they would not have heard of Morgoth at that point, and Bombadil would know that. So this made me wonder, is this fearless dark the period after Morgoth was cast down and before Sauron re-emerged as a force of evil?
Another possibility is the period where Morgoth was held captive in Valinor.