Windows 10 and WindowFX 6. Using the Opera browser. Latest version of everything. Nvidia GTX 970 and Intel Core i7 4790K.
After playing a video in fullscreen, when I press Escape to return to normal, the browser window becomes completely transparent rendering it invisible. The only workaround is to open the video in a new window (as opposed to a tab) and then press CTRL + W to close the invisible window afterwards.
It took me weeks to work out that WindowFX was the cause. I only noticed because I was using the feature that allows you to middle-click on a window to flip it and show process and resource information. Doing that also caused the window to become invisible. I accidentally did this today and realised that WindowFX was the cause.
I did work out a solution, but it is not ideal. I went to the "Animations" tab and the "Exclude an app" button and excluded Opera from WindowsFX effects. Now everything is fine. Note: I excluded the Opera launcher and the main executable as well.
Stardock support: You have presumably helped the fellow that asked about this in a different thread a couple of weeks ago. It would be nice if you would update threads with your solution so that we can all know what it is without having to send in a support ticket.
