Use `min-resolution: 2ddpx` media query for high-resolution graphics rather than/in addition to `-webkit-min-device-pixel-ratio: 2`, to allow non-webkit browsers to display high-resolution graphics.

I have tested this fiddle and found it to work in both Chrome and Firefox: http://jsfiddle.net/LRaJj/

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Alternatively, and perhaps even better, use unicode ▲ as up arrow instead of gif, as suggested earlier: https://news.ycombinator.com/item?id=4238956