Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

If you have problems with current Shockwave Flash plugin versions then check this:

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

Install this and use it

Flash block {web link} Never be annoyed by a Flash animation again! Blocks Flash so it won't get in your way, but if you want to see it, just click on it

Hi, Well, in safe mode it seems to work. It doesn't flash, I can scroll down and the video keeps smooth and the fans seem to be quiet.

About the other tips:

• I have a mac. I don't have graphic driver updates.
• That mms.cfg is that a mac thing? As I said, I already tried changing the dom.ipc.plugins.flash.disable-protected-mode to false. But it didn't help.
• I forgot to mention that I already tried to disable hardware acceleration. That doesn't work.

Now, it works with add-ons disabled (safe mode), but I only have java, flash and QuickTime (all updated) enabled.

One thing I've noticed is that I have 2 disabled plugins: Real Player and "Openh264". I can't delete them. I deleted Real Player plugin from my folder some days ago: mac>library>internet plugins but it created a new one again, so it's there (still disabled). The openh264 I have no idea how it got there, I don't have such plugin (that name) in my "internet plugins" folder, but it's there (also disabled).

So what can I do now? Thank you

mms.cfg = Flash Player

Go to your plugins page. Set everything video to Ask.

You could try disabling Flash plugin's protected mode. The protected mode feature of the Flash player plugin has security benefits, but seems to have compatibility issues on some systems. There is a new hidden setting for this: (A) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful. (B) In the search box above the list, type or paste flash and pause while the list is filtered (C) Double-click the dom.ipc.plugins.flash.disable-protected-mode preference to switch its value from false to true. This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox.

1) Enter the config by typing about:config in the address bar. 2) Enter media.mediasource.webm.enabled and press enter. 3) Right click on it and change to true, for some reason it is set as "false" which makes MSE & WebM VP9 not work properly. 4) Visit: https://www.youtube.com/html5 and check that everything is OK. 5) Try to watch a video. It should work now.

Well, I did what you said and it worked BUT then I undid it and it still worked.

So, now it works with plugins set to "always activate" and the "media.mediasource.webm.enabled set to false (like it was before)

and also with plugins set to "always ask" and the webm set to true (like you suggested)...

Go figure! I'll mark it as "This solved my problem" anyway :)

But I've changed my youtube to html5 (following your link)...maybe that's it?

Thank you

Could have been a corrupted file was at fault, and was replaced.

As long as it works. Safe Surfing. Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

Oops...Sorry FredMcD,

It only solved the problem with youtube videos. So I guess it was the html5

Facebook videos and flash banners are still flashing. I have all plugins set to "ask to activate" and mediasource.webm enabled.

I've tested other videos and thought everything was fine, but it's not.

I've called the big guys to help you. Good luck.

Thank you so much FredMcd.

Big guys...