Clear the cache and the cookies from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I've done those things already and they did not work. I am still unable to play any youtube videos past the 1 second mark. Same error message as before

You can check for problems with current Flash plugin versions and try these:

• disable a possible RealPlayer Browser Record Plugin extension for Firefox and update the RealPlayer if installed
• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
• disable hardware acceleration in the Flash plugin

• http://kb.mozillazine.org/Flash#Troubleshooting

Still no luck.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

Same issue here. On hundreds (!) of machines in the office.

Mix of Firefox 22/23. Flash from 11.3 to 11.8. All experiencing the same issue. No such problems with Chrome.

Resetting/reinstalling firefox brings no improvement.

Just to add:

We've tried enabled/disabled hardware acceleration, disabling protected mode in flash, clearing cookies and history, resetting firefox, reinstalling firefox from scratch, updating Flash plugin, disabling all the plugins in firefox, safe more...

So far no joy.

I've the same problem, I tried with a clean firefox's profile, disabling hardware acceleration from firefox and flash, disabling protect mode, installing an older flash's version, and nothing works.

I think that the problem is NOT firefox, because with the internet explorer I have the same probem, only videos in youtube, the rest portals like vimeo works correctly.

Make sure that your security software isn't blocking cookies.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

Hello cor-el, I tried your solution but I still have the same error

I found a solution for me................ Several weeks ago I added a SPRINT AirWave to my home network. They instruct you to install the AirWave (for efficiency) first off the cable modem, etc. and add your home network after the AirWave. I read on a YOUTUBE forum that putting the router first and moving the the AirWave to your router solves the problem. I did! It did! Thanks to Sprint for identifying the issue. You might not have an AirWave on your net but there might be something else in the path.

If your computer doesn't have any sound (no speakers hooked up, etc. then plug in a set of headphones and see if it works. I know it sounds funny, but I've been dealing with this problem for months on a work computer that has no speakers. Plugging in a set of headphones fixed the problem.

Youtube now requires a sound device present to work correctly.

Hello phantoms, I found the same solution yesterday. My coworker gave me a speakers and youtube worked fine.

That worked a charm! THanks so much!

I had same problem. I found a workaround is turning off Dynamic Adaptive Streaming (DASH) with Youtube Center (https://addons.mozilla.org/en-us/firefox/addon/youtube-center/)