Block Flash contents from playing automatically in Firefox

Martin Brinkmann
Aug 20, 2014

One of the most annoying things on the Internet are auto-playing contents. This can be a video that suddenly starts playing with or without sound, a bright flashy ad that makes you dizzy just by looking at it, or audio-only contents.

Not only can this be highly irritating considering that it is not always clear where audio may be coming from, but also because it is distracting and may impact the load of the system as well.

While click-to-play may be a solution for it, as it blocks all Flash contents by default, it may not be the ideal solution. For one, it does not block HTML5 video contents from being played on sites such as YouTube. For another, it may not reveal information about the content that the site wants to play.

That's where other specialized solutions may step in.

FlashStopper is a free add-on for the Firefox web browser that blocks Flash contents from playing automatically in the browser. While it is all about Flash, it can also block YouTube and Yahoo HTML5 video contents as well.

The add-on depends on the autoplay implementation of sites which means that it may not work on all sites that you try it on. With that being said, it should work on many different sites including some of the most popular sites on the Internet.

When you open a site with autoplaying contents, the add-on will block those before they start to play. When it comes to video, it will display a still thumbnail image of the video in question and a play button which means that you can click on the button to start playback immediately.

While it may be convenient to block auto-playback of Flash and HMTL5 contents on websites, you can customize that for some sites.

If you like to watch videos on YouTube for instance, you can allow the site to autoplay either for the session or until you revoke the permission again.

allow autoplay

Another interesting feature of FlashStopper is its proactive blocking functionality. This attempts to modify source code on sites you visit to alter the playback method to make it compatible with the add-on so that it can block autoplay contents.

Last but not least, it is possible to manage all site permissions to revoke them again.


FlashStopper for Firefox is a useful add-on for users of the browser who like more control over auto-playing video contents on the Internet.

While it won't catch them all, it takes care of many that you may be exposed to otherwise.

Is it better than click to play? That depends on how you use the browser and if you prefer to use the blocking of the extension over the plugin blocking. If you require HTML5 video blocking on YouTube or Yahoo, this is the add-on to get for that.

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  1. CHEF-KOCH said on August 22, 2014 at 3:50 pm

    Why we need a extension for that? From what I know Firefox supports click-to-play which means that I enable the content only after I explicit click on it. Click on the globe button on the address bar in FF, and under permissions ‘active plugin’ you can control the default behavior for the whole site. Or if you already use NoScript use enable noscript.smartClickToPlay in about:config and block/unblock the content you like. More plugins always means a higher security risk and of course more ram usage so it’s always better to use inbuild options first, and I’m sure a lot of Greasefork scripts can handle such behavior automatically if they detect */ in the site you visit (should also work with html5 content).

    1. Ray said on August 22, 2014 at 8:59 pm

      I’m in agreement with the usage of FF’s Click-to-play.

      I also use two helper addons that help with CTP’s usability – “Click to play per-element” and “Click to Play Manager”.

  2. Pierre said on August 22, 2014 at 2:49 pm

    Interesting but : an extension more !

  3. Robert Gagne said on August 22, 2014 at 1:14 am

    August 20, 2014 at 7:16 pm #

    Ficho wrote:

    I’m using Plugins Toggler add-on in Pale Moon/Firefox


    Thanks Ficho and thanks also to Martin Brinkmann for this excellent site.

    Robert Gagne
    Montreal, Canada

  4. mecase said on August 21, 2014 at 8:05 pm

    All the addons and methods you and the article have mentioned are totally useless. They don’t block the downloading of HTML5 video. They just stop the autoplay, but the videos keep loading.

    Currently it is IMPOSSIBLE to have a true Click to Play feature for HTML5 videos in Firefox. And why? Becuase the retarded Firefox developers don’t want to fix the media.autoplay.enabled preference.

    So blame the idiot developers of Firefox.

    The only thing you can do is to disalbe the whole HTML5 feature in Firefox with this preference:
    Then use blockable plugins like flash to play video content.

  5. Elben said on August 21, 2014 at 2:32 pm

    I use FlashBlock and am happy with it.

  6. Saad said on August 21, 2014 at 10:20 am

    for flash videos in Firefox just need go to Add-ons > Plugins and set flash plugin on “Ask to Activate”

    1. Tom said on August 21, 2014 at 3:06 pm

      The problem with that is that you need to click twice to play the video. Once on the video itself, and then again on the allow button.

  7. ilev said on August 21, 2014 at 7:41 am

    With Chrome I get both Flash & Html5 autoplay blocked with click-to-play.

  8. Lookmann said on August 21, 2014 at 7:06 am

    I am happy with Flash Block in FF .

  9. Tom said on August 20, 2014 at 7:40 pm

    I use the FlashBlock extension. It works well for both Flash and HTML5.

    1. Tom Hawack said on August 20, 2014 at 8:04 pm

      FlashBlock extension on what version of Firefox and/or Firefox fork, if I may ask?
      Because here with Pale Moon 24.7.1 (Firefox 24.7 ESR) FlashBlock wrecks the video frame, is not suited. It was the same when I was still with Firefox 24. FlashBlock is old and has always been late to follow.

      1. Tom said on August 21, 2014 at 4:25 am

        I use it on Firefox 31. I’ve never had any problems with it, but you’re right, it hasn’t been updated in a while. I just tried FlashStopper and it seems to be working well, I might just start using it instead.

  10. Ficho said on August 20, 2014 at 7:16 pm

    I’m using Plugins Toggler add-on in Pale Moon/Firefox and easily enable plugins when I need them.
    In IE11 I’m using ActiveX Filtering.

  11. Paul(us) said on August 20, 2014 at 6:20 pm

    Will having the Mozilla firefox 31 browser the Mozilla flashtopper add-on page is saying that this add-on is not available for firefox 25 ( This add-on is not compatible with your version of Firefox.) ? I do not understand?

    1. Tom Hawack said on August 20, 2014 at 6:29 pm

      That’s how it goes with add-ons but before the Australis madness it was sometimes possible to anti-date the add-on and have it run correctly. Since the Australis crisis many (not all) can absolutely not run on previous versions of the browser. Australis doesn’t like flexibility. Stick on your previous version would be OK if it weren’t for security (Australis also added security, 100% hell does not exist) or choose a Firefox fork such as Pale Moon, and forget those add-ons which stick to mommy.

    2. Martin Brinkmann said on August 20, 2014 at 6:22 pm

      Under version information it states Firefox 29 or later, strange.

  12. Tom Hawack said on August 20, 2014 at 6:03 pm

    The only plugin I have here on a x64 build (Pale Moon) is Shockwave Flash. I’ve set it to “Always ask” as default. I’ve also set plugin.sessionPermissionNow.intervalInMinutes to 0 to force asking on every launch. When a site requires Flash, if applicable I first authorize, have a look if the flash auto-starts and if it doesn’t I set authorize and remember. This is fine because I have only one plugin installed.

    Otherwise, a true pain when sites auto-start videos. I’ve even seen a page once with 5-6 videos all starting together, got mad, didn’t know (like when several phones ring simultaneously) where was what. In that case FlashStopper would be welcomed. At one time I was a user of Flashblock but it hasn’t been updated and with latest browsers it doesn’t work right anymore.

    Once again, some site administrators could think or take a nap.

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