The Blur effect description says: "Blurs the background of semi-transparent windows".
But it seems to only work for the Plasma widget Application Dashwoard, and does not work with other windows like Konsole of Firefox, or tooltip pop-ups.
Steps to Reproduce:
1a. Move a window with Alt key and mouse click.
1b. Move the mouse over some widget with a tooltip so that a pop-up appears.
1a. The window becomes transparent and has not blur effect.
1b. The pop-up is transparent without blur.
A transparent and blurred window.
The blur effect is active with the default settings.
The effect requires a hint on the region to blur.
Dupe'd to konsole bug, you'll have to file a bug against FF since it's not maintained here.
https://bugs.kde.org/show_bug.cgi?id=198175#c46 shows how to set a hint (from outside) for the entire window.
*** This bug has been marked as a duplicate of bug 198175 ***
Oh, so it is not forced by the compositor. The actual effect description seems to state that it is.
Shouldn't the description be updated to reflect that?
And what about a similar effect which does force blur all transparent regions? Or how could that be archived, a kwin rule?