Change opacity of single window
Solution 1:
I stumbled upon two possible solutions. In the Whisker menu, type "xfconf" and open the Settings editor, scroll down to "xfwm" on the left and then in the main table either
- disable
zoom_desktop– now you can alt+mousescroll on the titlebar of the window you want to be transparent
or
- enable
horiz_scroll_opacity– now you can mousescroll-sideways on the titlebar of the window you want to be transparent (I prefer this, that way I can still do alt-scrolling for zooming, should I ever need that)