unless stated otherwise, these are not-official-use-on-your-own-risk builds.
version 4.1.1
linux (64-bit): mozjpeg_4.1.1_amd64.deb (452 KB)
version 4.0.3
windows (64-bit): mozjpeg-v4.0.3-win-x64.zip (2807 KB) - official build
windows (32-bit): mozjpeg-v4.0.3-win-x86.zip (2502 KB) - official build
version 4.0.0
linux (64-bit): mozjpeg_4.0.0_amd64.deb (433 KB)
windows (64-bit): mozjpeg_4.0.0_x64.zip (1661 KB)
version 3.3.1
linux (64-bit): mozjpeg_3.3.1_amd64.deb (410 KB)
linux (32-bit): mozjpeg_3.3.1_i386.deb (406 KB)
windows (32-bit): mozjpeg_3.3.1_x86.zip (665 KB)
version 3.2
linux (64-bit): mozjpeg_3.2_amd64.deb (408 KB)
linux (32-bit): mozjpeg_3.2_i386.deb (405 KB)
windows (32-bit): mozjpeg_3.2_x86.zip (664 KB)
version 3.1
linux (64-bit): mozjpeg_3.1_amd64.deb (405 KB)
linux (32-bit): mozjpeg_3.1_i386.deb (457 KB)
windows (32-bit): mozjpeg_3.1_x86.zip (309 KB)
version 3.0
linux (64-bit): libmozjpeg_3.0_amd64.deb (403 KB)
linux (32-bit): libmozjpeg_3.0_i386.deb (458 KB)
windows (32-bit): libmozjpeg_3.0_x86.zip (308 KB)
version 2.1
linux (64-bit): libmozjpeg_2.1_amd64.deb (955 KB)
linux (32-bit): libmozjpeg_2.1_i386.deb (917 KB)
windows (32-bit): libmozjpeg_2.1_x86.zip (324 KB)
how to use (linux)
install the .deb via dpkg -i {name_of_the_downloaded_package}.deb
by default it gets installed to /opt/{lib}mozjpeg/bin/
so now you can do /opt/mozjpeg/bin/cjpeg -quality 80 foo.bmp > bar.jpg
how to use (windows)
extract the zip, open cmd.exe and navigate there via cd {folder}
now you can do cjpeg -quality 80 foo.bmp > bar.jpg
more information
you can find some instructions on how to use them on the mozilla blog.