I have to start by saying I run Windows, and there may be differences in how YouTube works on Mac vs. Windows.

For Firefox users on Windows, YouTube no longer uses Flash by default and instead uses an HTML5-based video player. Here's how to check what you're being served:

Right-click/Ctrl+click the player, and you should get a short context menu. The last line of the short context menu should indicate whether it's the HTML5-based player or the Flash-based player. If you get Firefox's regular context menu, it's not Flash.

For HTML5 video:

I think only Flash Control claims to be effective for HTML5 video, but I haven't tested it myself.

There is an internal setting you could try:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste media and pause while the list is filtered

(3) Double-click the media.autoplay.enabled preference to switch it from true to false

When I test that on YouTube, the pause button appears, since YouTube is triggering the video, but Firefox doesn't play it until I click the pause button and then the play button. Not the smoothest experience but perhaps useful until someone comes up with something better.

Thanks for your help, jscher2000.

I tried what you said. The youtube is, in fact, running HTML5, it looks like, from doing what you said in the top part.

I changed the internal setting, but that had no effect.

I will re-iterate, I am having the same problem in chrome, with the flash blocker I tried there. Could there be a non-browser issue I'm missing?

I tried updating flash on my system, but that didn't help. I also tried re-installing Java, but that didn't do anything either.

I am only mildly technical so I may be missing something really obvious.

https://addons.mozilla.org/en-US/firefox/addon/flash-control/ Controls as and when to display the Flash player and the HTML5 player.

Hi JCJHill, the HTML5 player doesn't use Flash at all, so you need a blocker that can block HTML5 videos. Other than Flash Control, I haven't heard of any.

Thanks for your responses.

As I've mentioned, Flash Control doesn't work either. I tried it in Firefox and Chrome to the same results. The behavior seems to be the same. I'll click to one page first on YouTube, and it will be blocked, then I'll choose a second video which won't be blocked.

Since posting this, I also tried Click-to-Flash in Safari 5. It seems to work on YouTube, but not on facebook videos.

Is there anything on my computer that would be common to Chrome and Firefox that might be causing the problem on both. It may or may not be also common to Safari.

Do you have any other video-related extensions? Perhaps you could test in Firefox's Safe Mode. That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the option key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any difference (assuming you still have the media.autoplay.enabled preference set to false) ?

I tried what you said, with the media.autoplay.enabled preference set to false

In safe mode, all the flash blockers are disabled.

There were some other extension that were disabled but said "could not be verified for use in Firefox." I deleted most of them except one I wanted to keep if possible.

One was the Adobe Contribute Toolbar. There was no option to remove it.

With the blockers disabled, video played normally, with out any blocking effect.

So, still no solution.

I restarted in normal mode and tested the video. Same result with the flashblock on.

If they are HTML5-based players, then I'm puzzled by the autostarting with that preference set to false. In Firefox 41, sites aren't supposed to be able to bypass that.

If they are Flash-based players, have you considered using the built-in Click-to-Play ("Ask to Activate") feature? To set "Ask to Activate", open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. Look for "Shockwave Flash" and change "Always Activate" to "Ask to Activate".

With this setting, when you visit a site that wants to use Flash, you should see a notification icon in the address bar and usually (but not always) one of the following: a link in a black rectangle in the page or an infobar sliding down between the toolbar area and the page.

The plugin notification icon in the address bar typically looks like a small, dark gray Lego block. (If it's red, Flash needs to be updated.)

If you see a good reason to use Flash, and the site looks trustworthy, you can go ahead and click the notification icon in the address bar to allow Flash. You can trust the site for the time being or permanently.

If you want finer control: This extension addresses the issue of only wanting some videos on a page to play: https://addons.mozilla.org/firefox/addon/click-to-play-per-element/ (I haven't tried it myself)

Do you have any external software on your Mac that intercepts video streams so you have the option to record them?

Ok... thanks again :)

So... for starters, I installed click to play per element, without changing the Shockwave Flash option. It WAS set to 'always activate', and stayed that way.

Then I installed an extension called YouTube Flash Player. This forces YouTube to play in Flash. When I did just those two things, the Flashblock plugin started working on YouTube exactly as it's supposed to. It did not work any better on Facebook. The fb videos still come up with the Flash block icon that is supposed to be clicked to play the video, but the video starts loading in the background with the sound playing.

Next I changed the shockwave flash setting to 'ask to activate'. On Youtube, this gave me the little grey lego you described. Clicking that, I was met with a second play icon, the Flashblocker operating as it's supposed to. Click through that and it works.

On fb, I'm not sure if it's working or not. The grey lego does not appear. The flash blocker play icon appears, but it is off center, and in the center of the screen there is a white radar-like icon that looks like it's loading, but it is not actually using my bandwidth yet (I'm watching in the moment using an app called surplus meter). If I click through the flash blocker icon I seemed to be able to play the video the first time, but repeat attempts left the video not playing at all. Might just be my connection in the moment.

So, at the moment, youtube seems resolved, and maybe fb, I'm just not sure. I'll keep you posted.

My problem may be solved, not sure yet, but is there any indication what's going on by what I described?

Thank you for the update.

Often embedded videos use a different domain, such as https://www.youtube-nocookie.com/

It seems to be a limitation of the "forced Flash" extensions that they work on youtube.com but not on that other domain, so you still get HTML5 for many embedded videos.

The videos I'm referring to on fb are not embedded youtube videos... those don't start automatically even without a flash blocker. I'm reffering to fb videos hosted by fb.

I want to be able to click to the page or lightbox where the video is displayed, and not have the video start loading.

My reason for this is that I often use a limited mobile data plan but I also create video content and I need to check comments and views on the videos without actually playing them and wasting bandwidth.