Flash upload to S3 doesn't work in Firefox 6

There is a reproducible example at: https://github.com/iwasrobbed/Rails3-S3-Uploader-Plupload

Firefox 5 it was working, but after upgrading to Firefox 6 it doesn't open the the file in flash anymore. If the domain is the same as the website, then it will work properly.

Under Safari, it works with same domain and S3 (a different domain).

The crossdomain.xml file I am using is this:

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedi开发者_运维百科a.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
  <allow-access-from domain="*" secure="false" />
</cross-domain-policy>

I'm getting an error from the above example that says:

"Error #2049"
"Security error."

This one has me stumped.

Edit:

After using tcpdump to see what was going on, it was communicating over HTTPS, even though I set the URL to HTTP. If I force the upload helper to set the URL to an HTTPS S3 URL, it works for Firefox 6. But I still don't know what has changed that made it be like this.