Carbon Emacs acts like emacsclient or gnuserv by itself, i.e. it only runs one instance and opens files in this instance from Finder automatically.

A drawback of this behaviour is that the usual server-window variable of gnuserv has no effect. When using elscreen to get tabs into Emacs the desired behaviour might be to open a new tab in the running Emacs when you open a file from Finder. This can easily be done, using my intelligent-kill command (see my elscreen posting) such that files from Finder are opened in a new tab, and you can close this tab with the usual C-x C-c:

And yet another Emacs hack: open an article from the Gnus summary buffer in another elscreen tab by pressing C-RET. Gnus does not support multiple article buffers for the same group, so I select the article below the cursor, rename the buffer to something else and restore the previous selected article. Works fine ™. Only drawback: most Gnus command like “reply” will not work, or more precisely they will be relative to the current article in the real *Article* buffer.

You like Firefox’s tabs to clean up your screen and keep an overview of which pages are open? Of course Emacs can do that as well: elscreen.
With the following code you can open new tabs with C-t and close them with C-x C-c (yes, the way you normally quit your Emacs; Firefox uses C-w which is used in Emacs for cutting text though). Every tab can be split into windows as you like of course.