(defun aragaer/use-chrome-for-next-url ()
  (interactive)
  (setq browse-url-generic-program "google-chrome-stable"))

(defun aragaer/browse-url-generic (url &optional new-window)
  (browse-url-generic url new-window)
  (setq browse-url-generic-program "firefox-bin"))

(setq browse-url-browser-function 'aragaer/browse-url-generic
      browse-url-generic-program "firefox-bin")

(define-key global-map (kbd "C-x g") 'aragaer/use-chrome-for-next-url)