Does it involve a cat playing below the search box on the built-in home page?

Those snippets cycle around and probably will be replaced by something else soon. If you reload the page (Ctrl+r) you may get one of the non-animated ones.

Some workarounds for now:

• Use a different home page. For example, perhaps you prefer Google as your home page? See: How to set the home page.

• Use a custom style rule to hide the "snippet" area below the search box. The rule would be similar to this:
  @-moz-document url(about:home) {
  #snippetContainer { display:none !important; }
  }
  and could be applied to the about:home page either by creating/editing a userContent.css file or using the Stylish extension.

More detail if needed.

Also see; https://support.mozilla.org/en-US/forums/contributors/710394 Lots of users don't like it when Mozilla changes the home page layout.

The answer is here; https://support.mozilla.org/en-US/forums/contributors/710394?last=60266#post-60294