Firefox – How to remove a website from the exceptions list for a plugin on Mozilla Firefox that is set to “ask to activate”

browser-pluginfirefoxflash-playeryoutube

I normally have Mozilla Firefox ask me before activating shockwave flash on
account of a slight bit of instability I notice when I tried to use YouTube. I
have it set to "allow and remember" on most websites, the main exception being
YouTube. Recently, however, I accidentally clicked "allow and remember" instead
of "allow now" on YouTube because I was tired and it had been a long day. Is
there any way to remove YouTube from the exceptions list without simply clearing
the exceptions list? I'm using Firefox version 29.

Best Answer

  • Go to about:config page and change devtools.chrome.enabled to true.

    Press Shift+F4 to open Scratchpad and switch Environment to Browser.

    Copy and paste the following code

    var ytprincipal = Cc["@mozilla.org/scriptsecuritymanager;1"]
      .getService(Ci.nsIScriptSecurityManager)
      .getNoAppCodebasePrincipal(Services.io.newURI("http://www.youtube.com", null, null));
    Services.perms.removeFromPrincipal(ytprincipal, "plugin:flash");
    

    Click Run and you 're ready!