When the tasks are grouped, due to lack of space, I can right-click and choose "Close All". But if there is enough space, and there are multiple windows of the same app, I have to close them one by one. I wish there is a way to close them all even when not grouped. For example, if there are ungrouped 4 Dolphin tasks on the task bar, clicking "Close" on the context menu with the middle-mouse button, not with the left-button, could close all 4 Dolphin windows at once.