I am having problems with my Udutu course. There are several slides I've created with voice over narration. I have uploaded that narration separately and when I view the course in Safari, some of the audio works on some of the slides but not others. Then, when I try it with Firefox, it works with the ones that didn't work on Safari, but not on the ones that did. Does that make sense? What can I do?

How are you recording the Voiceover files? as MP3's?  If they are recorded narrations as MP3 files, then you might try re-saving them from a utility such as Audacity, which you can download for free from http://audacity.sourceforge.net/download/ to be sure you are using a codec that all browsers will support.

If you are using TTS, why not just let the users read the screen with Voiceover, and enable the section 508 compatibility (on the "advanced" tab in the theme builder). If you want to use synthetic speech to record narrations, I'd suggest you purchase a higher quality voice from AT&T or one of those suppliers, to add more lifelike inflections than the ones in voiceover.