I am having the same problem and just realized that the videos load with no problem if using "private browsing". Checked the Flash setting in normal and private browsing and the seem to be the same.

I too have same problem and it works in private browsing. I don't know why.

you're right! thanks that was really driving me nuts. at least this way i can see vids until firefox does something about it :) Thanks!

This may not work for everyone, but I decided to clear my site preferences and youtube video playback went back to normal. Try it out, it might work for you too.

Hold Ctrl, Shift, Del Check the "site preferences" box Click "clear now"

This worked for me...Hold Ctrl, Shift, Del CHECK BOXES, cookies, cache and site preferences and then "CLEAR NOW"

This works........

thank you so much! this solved my problem, which was making me crazy!!!

i make as all tell me and nothing change. i make Hold Ctrl, Shift, Del CHECK BOXES, cookies, cache and site preferences and then "CLEAR NOW" and i open private browsing too but nothing changes and i dont know why, any one help me please Thanks.

I found a solution for me here http://www.google.com/support/forum/p/youtube/thread?tid=188ccea635a83962&hl=en&fid=188ccea635a839620004a77b30dd01ba Apparently Youtube put its videos behind a httpS link and if the browser URL is just http it wont allow the player controls to load. Just got to httpS://www.youtube.com and all URLs will be with the httpS and will load properly

The https seems to be the culprit. I've made a short cut to https://www.youtube.com and can see the videos from there. The above link on google support says something about adding Youtube to 'trusted sites' but I can not find a way of doing this in Firefox5

Window7, 64bit machine

Internet Explorer would play the videos okay but Firefox stopped viewing the YouTube videos some time yesterday for me. First I did a system restore to a point about 72 hours before the problem started. Didn't work.

Next I uninstalled and re-installed latest Adobe Flash. Didn't work.

I noticed Java had notified me of new update the same day the problem appeared. I installed the new Java. Now things work. I'm puzzled at the coincidence of failure at the same time Java notified an update.

Oh well, these steps I described were taken and things are working now.

Yes, the "https" works.

Tweaktube was causing the problem on my PC (Vistta, Firefox 5). I disabled Tweaktube and YouTube works fine now.

in my case is the "adblock plugin" after revise filter list and disable "http://s.ytimg.com/yt/swfbin/watch_as3-vflwQAc_A.swf" youtube works perfectly other option is using a "proxy server" like "hyde my ass" and this works fine

You solved my problem!! Very much appreciated.