I just made a small interface to the FLIF (flif.info) decoding library in Rust. This image compression algorithm seems to beat WebP for all kinds of images, and of course PNG and JPEG, while being losless. Moreover, any preface of the file is a thumnail of the final one. I felt it could be useful for Servo, even though it needs much testing and the algorithm itself is in heavy development.
Here is a video of PNG (adam7) vs FLIF: https://www.youtube.com/watch?v=ByH7RMsMxBY
And here is the repository: https://github.com/Razican/libflif_dec-rs