Congratulations on the new computer! If you visit YouTube's HTML5 test page, which boxes are blue and which are red?

https://www.youtube.com/html5

Also, are you using any YouTube-specific or video-related extensions?

Youtube currently uses the HTML5 player.

https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues

jscher2000 said

Congratulation which boxes are blue and which are red? https://www.youtube.com/html5

Red for "MSE & WebM VP9" I have some "downloader" extensions -- and they work; so I've been downloading whatever I want to watch but that's getting to be a PIA.

VerizonSucks said

jscher2000 said

Congratulation which boxes are blue and which are red? https://www.youtube.com/html5

Red for "MSE & WebM VP9"

That's normal, that last combination isn't enabled by default.

I have some "downloader" extensions -- and they work; so I've been downloading whatever I want to watch but that's getting to be a PIA.

Try disabling all YouTube-related and video-related extensions to see what happens with just default Firefox behavior.

OK I also had to install JAVA. Seems that Apple no longer builds it into the OS. Also did yet another Flash update. How often do they change that stupid app ?

But it still won't play. Example:

https://www.youtube.com/watch?v=IUc31f0A7CQ&feature=youtu.be

Got it !

Might have been the addon FlashBlock. It seems that it needs Java to run, so maybe re-installing Java required me to re-set the settings for FlashBlock...

The Java plugin is not used by many sites any more, mostly older games. You definitely should not need to use it for YouTube OR for the FlashBlock extension.

However, FlashBlock does have an option to block both Flash video and HTML5 video, so that may be the explanation.

Is there any security issue with HTML5?

VerizonSucks said

Is there any security issue with HTML5?

Maybe, but not that I'm aware of.

Any software can have an unknown vulnerability that opens the door to attack, so in theory a media file could be coded to exploit that vulnerability and do something unwanted (there's a wide range of potential types of attacks, from simply crashing the software to injecting malware onto the system). But... we don't know what we don't know, if you know what I mean.

I'm going to guess is was the Flashblock needing to be (re) set. Thanks.