Contested countryside allows the attacker to use the ability on the attacked province as if he was the defender. How does that interact with the general once per turn limitation of actions? Lts say i attack a shameful display. My opponent uses the action on his first action window. Can I now use contested countryside? If not the card would hardly be restricted, but why can I?

Both players are able to trigger actions on the attacked province, rather than the first player being able to “lock out” the second player from doing so.

I do not understand how that follows from the rules. There are two rules involved here. One is that you can only trigger abilities on cards you control. The other is that every ability is once per turn. How does voiding the first restriction automatically void the second?

Every ability is once per turn per player.

https://fiveringsdb.com/rules/reference#limits-of-triggered-abilities

"Unless otherwise specified, each triggered ability can only be used once per game round. "

"All limits are player specific."

Ok, thank you, I missed that second part.