There are a couple of prominent articles about how to do the "blur up" technique, or what can be described as loading a very small image in place of a big image (background, usually), then lazyloading the large version and using a blur filter to bring it into focus after the rest of page has... more.
Site Development & Funemployment
Mystery solved! Okay, this is a Drupal site and therefore I'm using CKEditor and IMCE as one does. But I wasn't seeing any buttons (or really any functionality at all) in the file browser window. I looked at all kinds of things as possible culprits.
Doing short-term consulting, sleuthing around files and systems, I feel like a spy. A special agent. It's like solving a crime. Something bad happened to these files. Something... wrong.