What player are you using?

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

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

tiburonjoan said

So I click on it and it plays in the other tab. But the original window and the familiar red YouTube arrow are GRAYED OUT and unusable. I don't know what's going on, but it only does this in Firefox. I'm attaching two screenshots, one showing the original YouTube video page, and the other tab page in which I play the video. Since when does YouTube make you open another tab to play a video? It should play right IN the same window at the page I selected!

First off I should mention that I am using an older MacBook. I have the current version of Firefox. I checked my Flash Player and I have version Shockwave Flash 17.0 r0 and I checked if there were any updates, and there were none. I did, however, install a YouTube Video Player and restarted Firefox. It seems to have worked, but we'll see. In the past few days it would appear intermittently, so hopefully I won't have to see it at all anymore. Thanks for your help.