Thanks. While no documentation, the source code can be found here (for future users): https://github.com/operasoftware/browserjs/blob/master/OPRdesktop/browserjs-25.0.js

I don't see how it relates to my video replacement problem, but at least now I know it isn't the browser script.

Opera 27 on Mac 10.10, not Opera 12. I ran a virus check and didn't find anything on my box.

My real issue is that there is no exposed documentation other than a 4 word description that overrides the javascript that was given by youtube. I have no issue with the need if it is needed, but why not have a more open view of the javascript. The link to localhost/browser.js doesn't show the code used. Google searching suggests others have seen it but Opera has not given any data about it. While I'm inclined to believe the end result isn't Opera's fault, that is hard to prove.

According to Opera, when I went to Jeff Atwood's blog ( http://blog.codinghorror.com ) , it had the following error:
Opera has modified script or content on www.youtube.com (PATCH-1185, youtube.com - show video above playlist). See browser.js for details (localhost/browser.js:65)

The video that shows up is a replacement of the expected video with a different video from hulu. Here is what it looks like:
http://postimg.org/image/yzeys1ykv/

My question isn't just why is this happening but why there are references to patches in the developer tools but no list of patches and descriptions available in from the Opera site. The only post I can find in this forum related to the issue does not provide anything useful.

I am using Opera 27 on Mac 10.10. I have also tried 12.17 on Windows and that did not show the issue. I don't have another Mac to try so I can also imagine the actual issue is on my Mac. But I still wonder why there is no documentation about the patch that Opera talked about. Oh and I spoke with Jeff Atwood and he has no idea why this is happening, so it isn't likely the server that is the problem.