If you are trying to get org-protocol to work under Ubuntu, the instructions will not work.
if you have tried to enable org-protocol under Firefox you might run
into the issue that firefox does not start emacsclient, no matter what
the about:config variables say.
After spending some time I discovered that this is an issue of Firefox's
integration with Gnome. What you need is to tell Gnome that you have a
new URI protocol called org-protocol, and that emacsclient is
responsible for it. This is done with the following two commands (be
careful to indicate the correct full path of emacsclient):