Ok, I tried the fixes that have been suggested again and I've got it working reasonably well now in Safari. I uninstalled Shockwave 11, and installed the Shockwave 10 FULL installer (not the slim, this was my mistake last time). I no longer get the flt ear error when I use the Rosetta Stone lessons online.
I found instructions here at Rosetta Stone Support.
http://rosettastone.custhelp.com/cgi-bin/rosettastone.cfg/php/enduser/stdadp.php?p_faqid=336&pcreated=1206737031
However, using the 'exit' or 'back' button (I can't remember what it's called- the one with the little guy in a parachute) from the lesson window, it apparently causes Safari to quit. So, don't use that button.
I don't get the error message anymore for Firefox either, but Shockwave doesn't seem to play properly and various images and buttons disappear, which isn't very useful. Maybe others will have better luck. I haven't tried it in Opera yet.