Perform the suggestions mentioned in the following articles:

• Clear Cookies & Cache
• Flash Plugin - Keep it up to date and troubleshoot problems
• Fix common audio and video issues

Check and tell if its working.

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

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

Thanks for the replies!

No, unfortunately I have not been able to solve the problem looking at those links. I have tried to deactivate several plugins and also run Firefox in safe mode but still the same problem. Don't knwo what to do. Aaah... frustrating.

From what I recall the problem started when I updated Firefox to a newer version some months ago.

If someone have hade the exact same problem and managed to solve, please contact me.

Hi again! It seems like problem is mainly with Youtube. For example Vimeo works much better. Any ideas?

A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

-> Firefox hangs or is not responding - How to fix

Check and tell if its working.

Thanks for replies.

I have tried to update my firewall (Zonalarm) and disabled Firefox, but without success. I guess it is another application that I should try to cut off, a media player plugin for example. Don't know which one that plays the Youtube videos...?

Perform the suggestions mentioned in the reply by cor-el.

Check and tell if its working.

Go to http://get.adobe.com/flashplayer/ and uninstall the flash player then reinstall the latest version.

I have tried to uninstall and reinstall Adobe Flash player. No, it didn't help. Thanks for the tip though.

I also tried to update my graphics card drivers to if that helped. Reinstalled Zonealarm firewall and also tried to run Firefox without having the firewall running at the same time to see if the firewall caused some problem. Nothing helps.

Aaah, it is sooo frustraing!

Any other ideas?

Did you try disabling hardware acceleration in your Flash Player settings? Right-click on any Flash video or animation , click "Settings" and uncheck “Enable hardware acceleration" in the Display tab.

Ref:

• Flash Plugin - Keep it up to date and troubleshoot problems under "Playing Flash videos makes Firefox hang"
• http://www.macromedia.com/support/documentation/en/flashplayer/help/help01.html

P.S. If you need a Flash video or animation to right-click, go here:

• http://www.youtube.com/profile?user=YouTubeHelp
• http://www.chemgapedia.de/vsengine/info/en/help/requirements/flash.html

Hi Alice! I have tried to disable the hardware acceleration but it didn't help. Thanks for the tip!

I thought this should have a simple solution. Have no idea how to troubleshoot this... Youtube works fine in IE so there is something with Firefox or some other application connected to it, but what?! So annoying.

Have you tried creating a new profile in Firefox?

Create a New Profile as a test to check if your current profile is causing the problems.

• Basic Troubleshooting - Make a New Profile

IF that New Profile works then you can recover your History, Bookmarks and Passwords from the Old Profile.

• Recovering important data from an old profile

Check and tell if its working.

Sorry, for late replies... It's not that I disregard you. Many things going on, so it's sometimes hard to find time for everything, like you probably know.

Thanks for the tips. I will try to create a new profile. But, first I would like to try some other things that I have thought about. I have experienced problem with Zonealarm before and I think I will completely remove it and all its components and see what effect that gives.

I'll keep you posted and tell how it goes.

Hi again! It seems like the problem solved itself... Probably by the new Firefox update or any oher plugin update that I have done the last week. I can watch Youtube videos without problems.

So, for now... I guess we can call this solved. But I don't know for sure what caused the problem and what solved it.

Thanks for posting replies and be willing to help me.

Over and out.

Thanks for posting back that you no longer see the problem after your recent Firefox and plugin updates. I'll mark this question as solved.