No thumbnails in the Files browser

In 4.0~beta2, when I open /usr/share/icons/hicolor/16x16/actions, I get no thumbnails in the Files browser.

Thumbnails should be display according to the preferences: Preferences → Search & Preview.

Feature Branch: bugfix/17062-image-thumbnails

Original created by @sajolida on 17062 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information