The first time you start Firefox, it reads in a whole mess of xul, html, css, and javascript. It parses it all and then dumps it to a binary file that can just

The first time you start Firefox, it reads in a whole mess of xul, html, css, and javascript. It parses it all and then dumps it to a binary file that can just be mmap'd back in next time. This is exactly like emacs, except that emacs also dumps out all of its own internal state including the state of the allocator; that makes it more fragile.