I realized a month or two ago that Flashblock had stopped working properly at Youtube and some other sites. It still blocked videos, but I couldn’t manually unblock them by clicking on them. For a while, I managed by temporarily disabling it when I needed to watch something. Today I went digging, and found that the cause has been discovered (interestingly, not a bug in flashblock) and is solvable.

It seems that Youtube changed their css or site design or something, and now they think it’s funny to put an invisible div over the top of the video. Clicks on the video are captured by the div instead, making it impossible to click on (and therefore unblock) the video itself.

The div has an ID of ‘theater-background’, and it is possible to get rid of it in Firefox’s configuration. Short version: Put #theater-background {display: none} in your userContent.css file.

Step by step procedure for people that need it:

  1. Open the Firefox menu and go to Help. In newer versions of Firefox, this is a little question mark button in the lower right corner of the menu, because the firefox UI designers are insane.
  2. Take the Troubleshooting Information option. In the winow that opens, look under “Application Basics” for “Profile Folder: Show Folder”. Click on Show Folder.
  3. In the folder that opens, look for a folder called chrome. If it is not there, create it.
  4. In the chrome folder, open or create a file called userContent.css.[1]
  5. Add the line: #theater-background {display:none} to the file. This will prevent the offending div from being displayed, making the video underneath it clickable again.
  6. Close and restart Firefox to make the change take effect.

I’m recording this partly so I can link it to people who need it, and partly so I don’t forget it myself when I need the information again. Original source here.


  1. Note that creating this file can be finicky if you are running Windows and have it configured to hide file extensions. Also note that hiding them is the default, which may well be the single most horrible misfeature Windows ever implemented.  ↩