Well, I at least have a workaround, but now I can't help but wonder why the error is only happening for me and not you or anyone else. Sure, it works with the third-party cookies enabled, but based on what you're saying it seems like I should be able to have them disabled without any errors.
I went back to the new "Test" profile that you had me create. I went into the preferences and set it to exactly what I have in my default profile (cache 1MB, third-party cookies off, etc.). I tried an embedded video, and it worked. So while the workaround with the cookies is functional, there is still a problem that exists that has not been solved.
I'm sure you know way more about Firefox than me. Do you have any idea what would cause an issue like this? I'm guessing it's a file in my profile folder, but I don't know which one (if any) to try deleting first.
Also, I just cleared out all my cookies (not the Allow/Block list, though) just to test, and that didn't help.
I'm not sure what could be causing this, but I guess the easiest way to fix it is to copy only the things you really need into the new profile. Install FEBE extension on both profiles, then create a selective backup of the old profile (not the full backup) choosing only the things you need like this:
To backup your extensions, use the quick backup feature and select the "Create single xpi" option like this:
It will generate a single installation xpi file with all your extensions.
When restoring these backups to your new profile, don't restore everything at once. Restore each file one-by-one, always testing the profile after restoring each file. This will probably allow you to pinpoint where the problem really is.
Let me know after which restoration the browser starts to behave badly.
I backed up my prefs, bookmarks, cookies, and username/passwords. None of those files were apparently the issue. I think I have most things back to normal, although I'm going to have to redo my AdBlock whitelist. Unless I can import the AdBlock preferences somehow. I'll see if I can figure that out on my own. (Seems like I have to go to the old profile, export my custom filters, and then import them in the new profile. Seems easy enough.)
So I'm in a fresh profile and everything seems to be working properly. Thanks again.
The problem has come back in the new profile now.
I really wish I knew the cause right now.
The only thing I can think of that I changed was setting up the .amz file type to open automatically with the Amazon MP3 Downloader. I don't remember if I set or changed a Mimetype around the start of April or not. I don't think I did... Would an error with the Mimetype settings really cause an error like this?
I don't think I did anything else beyond that.
Didn't help.
It confuses me why it's only happening to embedded YouTube videos. The videos work fine on YouTube itself. And no other embedded videos from other sites (Viddler, DailyMotion, etc.) are having problems. Only YouTube embedded videos. It makes no sense to me.
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