monline

Check out "System Settings / Window Behaviour / Window-Specific Settings". Here you can control (I mean limit) quite precisely what can or can't a window do that normally other windows can/can't. You can create rules containing filters (to control which windows do the rules apply to) and permissions/modifiers.

The latter is quite self-explanatory, but the filter rules are not. Probably you'll see some default rules, when you enter that settings screen (eg. for Firefox, Mozilla, ...). You can see that their filters contain a condition on the window's class. In Xorg (or X11) every window has a number of properties. One of these is their class which is a simple string. You can query the class of a window using the xprop utility. Start a terminal window, enter xprop WM_CLASS. The cursor changed to a crosshair that you should move on the window that you want to query, then click. Now xprop printed the class name(s) of the selected window in your terminal.