Maybe this helps you: https://www.reddit.com/r/kde/comments/18yi698/comment/kgkipgt/?context=3

Thank you so much. I have installed it, the script seems to do its work and everything works ... except Dolphin, I have tried several things but I can not get the blur and the background and all...

Which is the variant with the yellow folders? I downloaded all and it's not among them.

Fira Sans Medium: https://github.com/mozilla/fira

Yes, of course.