Personally Safari is the reason why some of my image-based sites still use JPG in parallel with WEBP. I think they fixed it just recently, but if you have an older mac (i do) Apple couldn't be bothered to include a WEBP codec with the OS. Firefox, Chrome and every other browser for mac supports WEBP but not Safari.

I think they resolved this in the last month, but I think for better or first Apple wants to roll out new SIMD instructions in their libraries much faster than Microsoft does. So at some point your CPU is too old. Of course the flip side to that in the Windows World is that people are stuck using a 10 year old instruction set. Intel doesn't seem to get it that by not supporting the latest AVX in their latest chips that people just "don't use AVX". If the latest SIMD instructions were widely supported you'd have a reason to buy a new computer, but when they aren't Intel has lackluster sales and wonders why.