Firefox seemingly very recently shipped their own titlebar controls buttons, which worsens even further the lackluster OS integration. In the screenshot you see my regular control buttons on the window to the left (default KDE Plasma theme) and the new custom buttons Firefox is serving now.
Would anyone know how to undo that change in about:config or anywhere else?
Are you using an icon theme? Papirus?
Yup, does that break something in the newest update?
Firefox is taking that icon from your GTK theme. And that’s the maximize button in the Papirus theme. So this is intended behavior.
You’d have to modify the theme or tell Firefox to use a title bar to fix it.
If Firefox is using GTK (GTK3 to be precise) to decorate the window, even in KDE, that might be some good news for him, altough I could be wrong bc I've never used Plasma for this long (30 days tops, long ago) to get to the point of wanting to change the title bar of anything. In Cinnamon (6.4.7) I'm using an old workaround for cases like this. It's still somewhat maintained. I can't guarantee it will work with Plasma but it doesn't hurt to try: https://aur.archlinux.org/packages/gtk3-nocsd-git After installation, open (or create) ~/.XSession and put these two lines in it:
export GTK_CSD=0 export LD_PRELOAD=/usr/lib/libgtk3-nocsd.so.0and reboot.This is how I've been replacing GEdit's CSD with a normal title bar, as well as Firefox's: