Upgrading the Found Frigate

[Barnacle Bill]

He's talking about the shielded worlds, some Fallen Empires have planets protected by an impenetrable energy barrier within their territory, once you have access to those worlds (most of the time by conquering the said Fallen Empire) you can unlock a research project to take down the barrier, it triggers when you scan the planet, once it's done, you can get one of four things :
-A mothball fleet of several battlecruisers and escorts fully equipped with FE tech.
-A technology vault which will give you access to a FE tech.
-A 5 stars immortal admiral who had been emprisonned for war crimes.
-Several hostile void clouds who had seemingly been emprisonned here (beware your science ship will probably be annihilated before it can get to safety)

Yes, shielded worlds, which come up not too differently from anomalies. In fact, until you said so I hadn't really noticed that they only come up in the (former) territory of a FE but I'll take your word for it.

Aside from the isolationist ones (who tend to get pissy about it), in my experience (on normal) I find that the FE's are pretty tolerant of your using frontier outposts to move systems without colonies from their territory to your own as long as you don't violate any of their pet peeves.

 

[Aed]

Weird, I was sure I got some debris tech off a destroyed frigate. Was ages ago though, was this changed in a patch or always there?

As far as i am aware it's always been the case that you can only salvage debris from ships your fleet has killed.