It's easy with Firefox: Right-click frame, select This Frame > Open Frame in New Tab.

But I get your point; there should be a one-click link to these pages, especially since some of them don't allow themselves to be opened in an iframe.

Ah, ok, that's why many are blank. I imagined that some of them may no longer be maintained, but then I actually tried one directly from pldb.info, and it worked. Well, typical I guess: vibe coded in 5 minutes and then uploaded without even testing it. Why am I even wasting my time writing a comment about this?