I added the alternativeContent div in the embed code, but then I removed it. I'm concerned to make any changes that might impact how my flash shows up in Firefox/Chrome, browsers seem to be allowing Flash content for arbitrary reasons which I cannot determine. Pixelsphere seems to be working in browsers so it's best I don't rock the boat!
You really need to have some kind of alternate content. Browser vendors want developers to move away from Flash Player, so they're doing what they can to make the experience worse on pages with SWFs. Some browsers will randomly pretend that Flash Player is not installed at all, even if it is. In that situation, if there's no fallback option, the visitor won't have a way to force the SWF to appear.
Here are the important details:
When the browser ignores Flash Player, you want to encourage the visitor to click on a link to https://get.adobe.com/flashplayer/. If they have Flash Player installed, the browser won't actually go there, but it'll ask if they want to activate the plugin. That will make your content load! If they don't have Flash Player installed, then the browser will continue to Adobe's website like before.
You don't necessarily want to say that your visitor doesn't have Flash Player installed in the alternate content anymore. Most people probably have it installed, but their browser is hiding it. Saying that it's not installed will look like a bug if they know they actually have it. I changed my fallback content to say something like "Click here to activate Flash Player" rather than "Click here to install Flash Player".