Maybe you like ball pens for doodling?
It can be that your browser changes the file name extension to PNG while downloading them, then you have to revert this and must rename the extension back to KPP before you can import them via ‘‘Settings’’ >> ‘‘Manage Resources…’’ >> ‘‘Import Resources’’.
This renaming happens, because Krita brushes are literally PNG-files with additional information describing the brush parameters, and some browsers want “to support” their users, thinking they’ll do us a favor renaming them for us. 
Michelist
Edit: Typo corrected