This image is using a .webp file instead of using a .png, it has transparency, it has lossless quality and only weights the 60% of the same PNG. Half size = double speed.
It also supports lossy compression (like a JPG) so, if you need transparency without the huge size of a PNG, which is a big deal. The Web developers were very happy in 2010 when google released this open standard.
It’s been 60 internet years and Mozilla still refuses to implement it in their browser, in a first moment they say they will come with a better jpeg format. Where is it? no one knows.
We can understand this way of doing things from Microsoft, or Apple (because they want a proprietary standard to make some bucks) but from Mozilla is a shame. More even they join this companies supporting .h264 video format.
So, when someone ask me which browser is the best I’ll go with chromium, for this and other reasons.
Ah, in the case you are in Firefox and you are seeing the image is because I added an HTML5 fallback with the two images (PNG/Webp). Don’t fool yourself, it works but is far to be a solution, you are still downloading a big PNG and I had to upload 2 images.