In bug 1381084 we discovered that setting a priority on an image request based on layout comes too late. HTLM parser creates a preload for every image that it hits in the markup. It's possible this just leads to an exceeded demand on bandwidth. Delaying these preloads may give a chance to set better priorities.

This doesn't really bring a visible win. On some facebook pages I was able to actually reliably slow things rather down than up when the preload count was throttled to 0, threshold to get the original load time was about 20 preloads. bbc, cnn, nytimes was not getting better at all. Anyway, fiddling with this a bit through WPT could show if there is some objective difference.

If there is anything to do about images, it needs a broader discussion and some preliminary testing/analyzes.