When looking for things that delay a web page’s render start time, there are a number of usual suspects. Blocking scripts. Oversized CSS files. Possibly a big base64 encoded image at the top of the page.
We don’t normally think of favicons.
CSS background images tend to be loaded and displayed later than images referenced in <img> elements. As a rule, they’re given lower priority by the browser, and the CSS has to finish loading before they can be discovered (making them invisible to the browser preloader).
Last week, we heard about a small but potentially important bug fix in Chrome (thanks for @smashingmag for Tweeting about it):