None of the other solutions worked for me. This one did.

i had problems with flash and after reinstall my antivirus software its ok

try to reinstall your antivirus software

un-check or remove this: ||youtube.com^ from the adblock scripts

I had this problem too. I just tried to see if an add-on was causing the problem. One of them was. I disabled it and now the problem is fixed. :)

Add-on that caused the problem: TweakTube 1.0.7

Turning off hardware acceleration on flash didnt work Clearing cookies/etc didnt work BUT disabling ADBLOCK PLUS on the webpages affected DID work (right click on their icon in the toolbar and click Disable on this page). Thanks Adblock, used you for years but you're history if this isnt fixed soon.

I saw a post saying to disable adblock. So I did and it worked, then I turned adblock back on and it was still working. So I guess you can try disabling adblock then enabling it.

no need to disable adblock totally just click adblock icon in address bar (or wherever it is on yoour browser page and click block on youtubes page. damm glad i found this thread had been using chrome for watching youtube till i found this thread. Now back with firefox the only browser that i want to use.

I had the same issue, Deleting just the youtube cookies from firefox worked for me, I can now see youtube videos again in Firefox!

Same here.. Cannot play any video from Youtube directly, but works if the video comes from facebook regular or Safe mode = does not work... Private Browsing Works !! - But not very convenient !!! Other Browsers work fine as well. Delete cookies and recent history did not help. I even re-installed Flash player V10. No luck. Windows 7 64 bits. Firefox 8.0

I had to click forbid youtube.com from no script to make it work.

Sir... The easiest way to get rid of this is update your Adobe Flash Player. Please visit: http://get.adobe.com/flashplayer/ and download the latest version of Adobe Flash Player & install it! VOILA!! You're good to go!

same problem here. click "view" on toolbar. click on "adblock plus, blockable items" in the dropdown menu. this will show what is being blocked on the website. in the case of youtube, click on whatever ends in ".swf" and add a filter to make an exception. after the filter is added refresh the page and the video should start up again. i use a macbook pro.

Disabling ADP fixed it for me. Many many thanks

http://bitrim.org/post/14122023085/bitrim-alpha-2-preview

I don't get a completely black screen. I can see the white text and play button, but neither do anything when clicked.

It's the HTML5 player that's been embedded so is not a flash problem.

Safe mode with all addons disabled does nothing.

Videos on the YT site itself work fine.

Ok... I had the exact same problem... I tried everything you guys suggested without success... then I remember I had blocked something from youtube with adblock. So I went into Adblock settings and removed any personal filter I created (there were only 2 links, both from youtube). After that youtube went back to normal, working correctly, without any adds!

I'm pretty sure it was Addblock, since as soon as I tried and deactivate it, youtube would start to work again... but with AAAAALLL the adds!!! So try this out! Worked fine with me!

I had this same issue until I disabled some plugins that I didn't even know were on. Go to Tools> addons> select plugins tab on the left. I disabled Adobe Acrobat, Getplusplus for Adobe, Foxit Reader, Microsoft Windows Media Player, and all others EXCEPT: DivX VOD, Java, Quicktime and Shockwave plugins (about 2 or 3 of each are listed and enabled). I went to youtube and voila - videos work perfectly again - no more frustration. I didn't need to clear history nor cache. I don't use adblock or any adblocking software/addon. Hope this helps.

why should i have to try all this stuff when there is absolutely no problem in IE8, how do i get an older version of firefox PLEASE

You have turned on AdBlock. You can't turn ads off on YouTube or you will also turn off the videos. Just play with changing your AdBlock settings.

Change your adblock settings... you can't turn off ads on YouTube or you will turn off the videos too.