Installation Problems
  • Installation dialog box does not appear when you click on the install link.

    You may have to put as well as in your whitelist.

    In Firefox do Tools->Options->Web Features->Allow websites to install software.
    Then click on the [Allowed sites] button and enter the site you want to allow Flashblock to be installed from.

  • Download error when trying to install flashblock.

    Sometimes the mirror you are redirected to has problems. What I generally do is to manually go to This will actually redirect you to one of the mirrors. If this mirror is down I try again. Odds on after a few attempts you will be redirected to a working mirror. You can then install (or download) directly from this mirror.

  • Chrome Registration Error when trying to install Flashblock.

    You get one of the following errors:

    Chrome Registration failed for Extension '{3d7eb24f-2740-49df-8937-200b1cc08f8a}'
    when calling nsIXULChromeRegistry::installLocale with this chrome path:...
    Install failed. There was a Chrome Registry Error: -239
    Install failed. Could not performInstall. Error code: -239

    This can happen if you have an older version of Flashblock installed. If you get this error, you will first need to fully uninstall flashblock. In Firefox you may need to start in safemode before you can access the Extension Manager to uninstall Flashblock.

    If this doesn't work and you are using SeaMonkey 1.1.9, one of our users reported that this procedure worked for him:

    User Contributed solution Note: How to locate the SeaMonkey profile Folder.
    1. Having used mnenhy to uninstall existing FlashBlock, restarted Seamonkey and attempted to install FlashBlock139 and finished with the -239 error
    2. Close Seamonkey
    3. Copy the ProfileName\?.slt\chrome\overlayinfo to a new name (eg ProfileName\?.slt\chrome\overlayinfoOld) and then delete the original directory ProfileName\?.slt\chrome\overlayinfo
    4. Start Seamonkey
    5. FlashBlock is actually installed and working so it looks like something in the files in the overlayinfo sub-directories that is causing the chrome Registration problem.
    6. Having checked that FlashBlock is working Close Seamonkey.
    7. Copy the overlayinfo directory back to original name eg ProfileName\?.slt\chrome\overlayinfoOld back to ProfileName\?.slt\chrome\overlayinfo
    8. Restart Seamonkey FlashBlock 1.3.9 is working :-)
    Our Uninstall Guide can be found at:
Known Problems (General)
  • Reflow bugs in the Gecko Rendering Engine There is a bug in the core code which causes Firefox 1.0 and Mozilla Suite 1.7 to crash when viewing certain websites. This bug is fixed in SeaMonkey 1.0 and Firefox 1.5 but not in Firefox 1.0. For further details, please see mozilla bug 228557

    A flash object in an absolute positioned div will cause another reflow bug. For further details, please see mozilla bug 194952

    Flashblock contains a workaround that should reduce the possibility of triggering these bugs.
  • Flashplayer Plug-in not installed
    If you do not have the Flashplayer plug-in installed, but have installed Flashblock, Firefox/Mozilla may crash when you visit webpages that have flash content.
  • MacOSX and Java Embedding Plug-in 0.8.8 installed
    If the Java embedding plugin was installed when you try to install Flashblock, on restart Firefox will consume CPU and never finish loading. Uninstall the JEP before installing Flashblock. Restart Firefox twice, then reinstall JEP.

    Or follow the instructions in Sourceforge bug id 1081427 to temporarily disable the JEP.

    This problem does not affect newer versions of the JEP including the versions shipped with Camino 0.9, Firefox 1.5, and SeaMonkey 1.0.

Known Problems (Firefox and SeaMonkey 2.0+)
  • Javascript must be enabled to use flashblock.
  • Firefox 1.0.x and Netscape 8.0.x must be restarted twice to install/uninstall flashblock.
  • Kerio Personal Firewall rewrites the incoming HTML preventing Flashblock from detecting Flash content
Known Problems (Mozilla Suite and Seamonkey 1.x)
  • Javascript must be enabled to use flashblock.
  • Mozilla must be restarted twice to install flashblock.
  • No uninstaller. Please see our Uninstall Guide:
  • Kerio Personal Firewall rewrites the incoming HTML preventing Flashblock from detecting Flash content
Known Problems (Netscape 8)
  • See: Known Problems (Firefox).
  • If you drag the Flashblock toolbar button out of the multibar tray (using View->Toolbars->Customize...) and on to a toolbar, subsequently trying to customize the toolbars again will result in and empty multibar tray and not being to move any of the buttons all ready on the toolbars. Either click on the "Reset All to Default" button; or download and install multibarfix-0.1.2.xpi which fixes a bug in the Netscape multibar code.
Known Problems - Extensions interfering with Flashblock
  • Adblock/ AdblockPlus: Turn off Object Tabs in the Adblock options.
  • NoScript: Use NoScript's built in Flash blocker instead.
  • UnPlug: to turn on support for FlashBlock, go to the options and check the "Use FlashBlock" box on the first page, then restart FireFox.
  • iMacros for Firefox: Uninstall or disable iMacros.
  • Stop Autoplay: 0.4.2 will disable Flashblock. Please use 0.4.3 or later.
  • Toolbar Buttons contains a flashblocker that interferes with flashblock. In addition the Toolbar Buttons flash block button is buggy. Uninstall or disable Toolbar Buttons.
  • Pearl Crescent Page Saver prevents blocked flash videos from being unblocked and played. Disabling the Page Saver preference pagesaver.flash.arangeToCapture allows blocked videos to be unblocked and played. Thanks to user GodforalL for this tip.

For questions or comments about flashblock, please send a message to the flashblock mailing list.
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