Update your Flash Player Version 19.0.0.185
https://www.adobe.com/products/flashplayer/distribution3.html Note: Windows users must download the “Internet Explorer” and “Plugin-based browsers” installers.

Note: Edge on Win10 does not use ActiveX version but its own Flash.

See if there are updates for your graphics drivers https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

Issues have been previously linked to the McAfee Site Advisor extension. Try to disable it and see if the problem persists.

http://service.mcafee.com/faqdocument.aspx?id=TS100162 How to uninstall SiteAdvisor

To disable it: Type "about:addons" in the Location bar Find the extension and click on its "Disable" button

Thanks -- updating Flash solved this problem.

Glad to help. Safe sufing.

This problem has now returned all of a sudden, without anything else changing -- any advice? YouTube videos were playing fine half an hour ago, now nothing does.

I am sorry to hear that  :-/

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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

I've been having the same problem watching Youtube videos, and after going round and round with uninstalling/reinstalling Adobe Flash, etc., etc., I stumbled upon this article: http://thenextweb.com/insider/2015/07/14/firefox-rings-the-death-knell-for-flash/

I've also (perhaps coincidentally) been having problems watching PBS videos when I never had problems there either. Something fishy is going that either no one knows about, OR won't say because too many people are having the same problem, with no solution.

Melon said

I've been having the same problem watching Youtube videos, and after going round and round with uninstalling/reinstalling Adobe Flash, etc., etc., I stumbled upon this article: http://thenextweb.com/insider/2015/07/14/firefox-rings-the-death-knell-for-flash/ I've also (perhaps coincidentally) been having problems watching PBS videos when I never had problems there either. Something fishy is going that either no one knows about, OR won't say because too many people are having the same problem, with no solution. PS I can watch Youtube videos just fine using IExplorer...AND, the advice to "refresh" Firfox to solve that problem only served to lose all my add-ons, bookmarks and passwords, for which I'm now paying dearly....

Refresh Firefox {web link} is a LAST RESORT ! !

Refresh Firefox - reset add-ons and settings

If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its default state while saving your essential information like bookmarks, passwords, and open tabs.

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences

Melon said

I stumbled upon this article: http://thenextweb.com/insider/2015/07/14/firefox-rings-the-death-knell-for-flash/

That is a very old article. The current flash is safe.

• 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

OK, so this has just happened again right now. After a morning of browsing normally and playing videos, all of a sudden nothing plays. Someone asked for a screenshot, so here's a really helpful image of YouTube not working -- the loading symbol just turns around.

This *never* happened until the Firefox update.

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

A new version of flash came out yesterday, not to throw a monkey wrench (yesterday). Please update your plugins to the latest version. Check to make sure you are up to date:

• https://www.mozilla.org/en-US/plugincheck/

If you see any issues also see:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems