Firefox doesn't use the KDE file picker by default. You can set widget.use-xdg-desktop-portal.file-picker to 1 to use the desktop environment's native picker.
It all comes from a blog post from 2021. A picture from it went viral on X/Twitter a week ago. (First two links in the article) Since then everyone is posting it.
Actually, the top one is the logo of the chromium browser engine, but the bottom one is not the logo of the Gecko browser engine. That's the logo of SpiderMonkey, Firefox's Javascript engine (Chromium uses V8).
Firefox doesn't use the KDE file picker by default. You can set
widget.use-xdg-desktop-portal.file-pickerto 1 to use the desktop environment's native picker.https://wiki.archlinux.org/title/Firefox#KDE_integration