Ephera

Hmm, thinking about it now, I actually don’t have much beyond the Breeze (Light/Dark) themes preinstalled either. I have the openSUSE themes, because I am on openSUSE.
Aside from that:

• In Window Decorations, there’s the Plastik theme.
• In Application Style, there’s “Fusion” and “MS Windows 9x”.
• In System Sounds, I’ve got “Ocean” and “FreeDesktop”.
• And in “Login Screen (SDDM)”, I have “Elarun” and “Maldives”.

I believe, the Oxygen themes got removed from the default themes, possibly with Plasma 6.
But yeah, maybe you also just had additional theme packages installed. The Arch Wiki lists some of those, too.

The Arch Wiki says you should install it via the plasma-meta package for a full-fledged installation, and just the plasma-desktop package, if you want a minimal install. Is that maybe where you chose the wrong one?

With the application focused, press Alt+F3 to bring up the window menu. In there, under “More Actions”, you can uncheck “No Titlebar and Frame” for temporarily changing this.

But you’re probably interested in permanently changing it. For that, select “Configure Special Application Settings…” instead.
In that window, click “Add Property…” and select “No Titlebar and Frame”. Then change “Yes” to “No” in the newly added line and click Apply.

This changes it for that one application. You could also tell it to render a titlebar for all windows (with potentially unforeseen consequences) by changing the “Window class” dropdown to “Unimportant” and selecting “Normal Window” in the “Window types” dropdown.
If you change it like that, you can find this rule in the System Settings under “Window Management” → “Window Rules”.

Ah, neat. I had to come up with my trick, because I wanted to know specifically which line changed to what. That’s pretty easy to see with git diff then. But yeah, if you just want to know which files changed, that’s certainly saner. 🙃

A trick you can do to find out individual settings files, is:

1. In your ~/.config folder, run git init.
2. git add .
3. git commit -m "Initial commit"
4. Change a setting in the GUI.
5. Run git status or git diff to see which file got changed.

You can then run git restore . and repeat from step 4.

If you’re done checking settings, just delete ~/.config/.git/.

What is this article talking about? That’s a UX change. It has nothing to do with privacy or Mozilla’s commitment to privacy.