Comment # 9 on bug 1155387 from Alexander Shchadilov

Another workaround for this is adding custom rules for each problematic app in
Plasma settings.

1. Launch a GTK application.
1. In Plasma, go to System Settings/Application Style/Window Decorations/Theme,
click on an icon in the left lower corner of Breeze-styled window to get
"Breeze - System Settings".
2. Window-Specific Overrides, Add, Detect Window Properties, click on the
window of application from step 1.
3. Press Ok.
4. Set Border Size to "No Border" and check "Hide window title bar", press Ok.
5. Press Ok to close "Breeze - System Settings".
6. In System Settings, go to Window Management/Window Rules, New, Detect Window
Properties, click on the window of application from step 1.
7. Press Ok.
8. In Appearance & Fixes, set "No titlebar and frame" to "Force", "No".
9. Press Ok.
10. Press Apply in Window Rules.