The Firelands Province is the Rihannsu-English translation of R'aemn dh-Llaiir, the Tholian Territory. Naturally, the Romulans don't refer to it as 'Tholian Space', regardless of what the sensors output, since it is under Romulan ownership.
A year after the absorbing of Tholian Space, Rihannsu patrols would often experience severe psychological trauma in certain areas. Extremely powerful images would consume them, rendering them unfit for duty. Typically, these phenomena would affect only a handful of the crew at a time, allowing for the remainder to safely get the ship out of range. Eventually it was realized that these events were due to psy 'reflections' from the previous residents....pools of collected psy resonances that collected and plagued lifeforms that passed through them. Markers were placed near the strongest of these to warn other ships, most of which were placed by the crew of the ChR Hvakh, which was the vessel assigned to patrol that area and the nearby Klingon border.