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, server-mode JPG output is encoded with MozJPEG automatically — there is no separate switch — and browser-private mode uses the browser’s own JPEG encoder instead. Pair it with sensible dimensions and optional EXIF stripping for form and email workflows that require JPG.