How to cache images in GeckoFX

I use GeckoFX to render some web application's GUI. There are many repetitive small 16x16 images here and there injected into single HTML page by javascript.

All these IMG instances are downloaded one by one from the web server and I couldn'开发者_如何学Pythont optimize this behavior using cache-control or expires headers or by using javascript Image(). So rendering is ultra slow and dirty comparing to Chrome or IE.

How can I make GeckoFX to cache or preload a couple of small images?

It's done by replacing all images with spans. Those spans are now using css classes with background-image and floating.