When Captivate publishes HTML5, it doesn't work in Firefox. Captivate exports only MP3 audio, and Firefox only plays OGGs. This post provides some tweaks for the Javascript to get rid of the error message and look for OGG versions of the file when needed. You have to create both versions of the audio files.
How To Choose An Authoring Tool For Your HTML eLearning Development | The Upside Learning Blog
Comparison of Lectora, Storyline, and Captivate. Some good details I haven't seen elsewhere, like how each program loads the framework and content and how that affects performance. A few inaccuracies (you can still create a non-ADA compliant course in Lectora even if you check the 508 box, for example).