Safari 6.0.4 Cannot Play Google Voice Voicemails

Question

I've been troubleshooting this problem for far too many hours, and I am at a loss. I've tried everything other than reinstalling the entire system. Instead of doing that, I'm switching to Chrome and posting here in the hopes of finding a better solution.
The problem: Safari will not play google voice embedded audio voicemail files.
The voicemails show up with a play icon and a time; when you click on them, the graphic changse to an audio file progress bar, but the file never plays.
These voicemails WILL play in Chrome and they WILL play in Firefox.
More frustratingly, they will also play on my wife's iMac that is also running all updated software (OS X 10.8.3, Safari 6.0.4, etc.), and on my own iOS devices with Safari.
Background
I'm running 10.8.3 on a 2.7ghz core i5 27" iMac.
I have updated to the newest OS and all software updates.
I'm running the newest version of Flash and Java, and all are functioning properly.
I've uninstalled flip4mac and anything else that I thought might conflict with playing audio files.
I've reset safari numerous times, booted into safe mode, restarted numerous times, emptied every cache under the sun, repaired permissions, run daily/weekly/monthly updatesa in termina, and tried disabling all internet plugins. Nothing works.
Current Understanding/Knowledge/Conclusion
These files are NOT using any plug-ins to play, but are just using standard html5 audio tags. My wife's computer will play the files fine even with the quicktime plug-ins disabled. They DO use javascript to switch to the full audio player progress button, but I don't think javascript has anything to do with playing the actual file. Note: Firefox plays the files differently and it depends on Flash to play them; but I don't think that's the case with Chrome, and both Chrome and Safari are webkit browsers. Safari is unique in being a 64 bit webkit browser, and I'd be willing to chalk this up to it just not working in Safari – but it works just fine on my wife's machine.
Any solutions, ideas, or even troubleshooting tips would be welcome. As I said at the outset, the only next step I can see is reinstalling ML, and I'd rather just switch to Chrome than do that...

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this test is to determine whether the problem is localized to your user account. Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your personal files or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault in OS X 10.7 or later, then you can’t enable the Guest account. The "Guest User" login created by "Find My Mac" is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.