MozJPEG
MozJPEG is an improved JPEG encoder originally from Mozilla. It aims to produce higher visual quality at a given file size—or smaller files at a given quality—compared with many default libjpeg builds, especially for photographs. It remains a JPG encoder: output is still standard JPEG that any JPG decoder can open.
Techniques include better quantization and progressive scan options tuned for the web. MozJPEG does not replace WEBP or AVIF; it improves the classic JPG path when compatibility demands JPEG. Not every hosting environment ships MozJPEG; when unavailable, FileShrinkr falls back to standard JPG encoding.
On FileShrinkr, enable Sharper JPG (MozJPEG) in Server mode when the option appears and your output format is JPG. Browser-private mode does not use MozJPEG. Pair MozJPEG with sensible dimensions and optional EXIF stripping for form and email workflows that require JPG.