TYPO3 Core

I think that some things get mixed up here. There actually is a problem with Option-Space on Mac, but part of the descriptions of Helmut is not an error:

With Firefox, hitting option+space before or after a normal space inserts a nbsp; ...

In RTE putting a second space before or after an existing space ALWAYS creates  . This is necessary because multiple consecutive spaces in HTML always get collapsed into one single visible whitespace. So hitting Space multiple times would actually advance the cursor only once, and to make the usage more intuitive for editors the RTE automatically transforms adjacent spaces into  .

The bottomline is that with multiple spaces you do not have to press Option at all to get a  . Just hitting Space multiple times results in one space followed by several  .

The real problem - at least to my research - is that Option-Space does not work AT ALL in RTE on Macintosh (as described in related bug report 10127). Currently Option-Space just behaves like hitting the sole Space bar on Mac.
I guess that Helmut's trials to insert   did succeed sometimes only because occasionally he inserted multiple spaces and the RTE transformed some of them into   as described above.

On all my test I could not find a single instance where Option-Space created a   when used in the middle of a word (not adjacent to any other space). This did not depend on the browser used. It is a general problem, probably related to the OS (Option-Space might be reserved for Spotlight) or to a general flaw in the JS code of HTMLArea on Mac.

Please try the patch attached to issue #10127 with Safari on Mac after applying the patch attached to issue 0010324.

Make sure to delete all files from directory typo3temp/rtehtmlarea and to clear the browser cache before testing.