user.js with
these set; read for installation and preferences details)-no-remote and -P command-line arguments when you
run Firefox to use a "clean" profile (one where you don't care if things in it break).
Note that -no-remote is new to Firefox 2; older versions should set the
environment variable MOZ_NO_REMOTE=1 (changeable in System Properties on
Windows, one of export or setenv at a terminal window on
Mac/Linux).