The stub installer is the default installer interface that most users installing Firefox will see. It’s a tiny download (200-300 KB), so it gets the user into the product experience quickly. It’s also a highly streamlined experience; there are no options or prompts offered, except in the case of a returning user (see Profile Cleanup). Running the stub installer immediately starts downloading and installing the browser, and automatically runs the new installation and exits when it’s done.
An Install Ping is sent when the stub exits.