moz-reload-mode.el

(require 'moz)

;;; Usage
;; Run M-x moz-reload-mode to switch moz-reload on/off in the
;; current buffer.
;; When active, every change in the buffer triggers Firefox
;; to reload its current page.

(define-minor-mode moz-reload-mode
  "Moz Reload Minor Mode"
  nil " Reload" nil
  (if moz-reload-mode
      ;; Edit hook buffer-locally.
      (add-hook 'post-command-hook 'moz-reload nil t)
    (remove-hook 'post-command-hook 'moz-reload t)))

(defun moz-reload ()
  (when (buffer-modified-p)
    (save-buffer)
    (moz-firefox-reload)))

(defun moz-firefox-reload ()
  (comint-send-string (inferior-moz-process) "BrowserReload();"))

This reload-as-you-type behaviour is actually intended. I find it very convenient.
Here's a slight modification of the above code which restricts reloading to trigger only when the buffer is saved.
moz-reload-on-save-mode.el, https://gist.github.com/666092