See if this helps;

https://support.mozilla.org/en-US/kb/flash-video-wont-play-full-screen

Thanks for reply but that didn't help, as I said software wise everything is up to date and the problem is I can't view specific type of videos like Vevo or official music videos.

Is your java updated?

If not go here https://java.com/en/download/index.jsp

I am not using JAVA. But to check it I just installed it and it didn't help. Also I uninstalled Flash Player but now I am getting "An error occurred" error immediately after clicking on the videos that were not working, other videos are still working.

Hello try to install Java on the extensions.

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences<Enter> in the address bar

Select Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

@Brandon Vita As I said in the post above Java didn't help.

@FredMcd I tried those options yesterday, they didn't help.

Try reinstalling and in safe mode

Already reinstalled everything that is possible, still the same.

Even system restore didn't help. Its really baffling.

Some videos play but some do not. Please copy some of the web addresses of the ones that don't work so we can look them over.

I have not tried this, but take a look at it;

Video WithOut Flash {web link} Watch videos without flash

Go to the web page. Once the page is loading, mouse to the address bar and Left click the icon. A window for displaying site information should come up. Select More Information. Now select Permissions. In the menu, go thru the list. Unselect Default, and manually set everything to Ask or Always. The top of the list are the plugins. Do the same with the other settings also.

When you are done, hold down the shift key and reload the page.

Any changes?

I installed "Video Without Flash" add-on and I am getting "This page isn't available" message while trying to watch those videos that I can't watch with flash. Other videos are still working. I also tried what you suggested in your last post and it didn't help. Those videos that I can't watch in Firefox are working on Internet Explorer but they are starting to play after loading for 10 seconds, while other videos are starting immediately.

Please post the addresses so we can check them out.

For example:

http://www.youtube.com/watch?v=dvgZkm1xWPE

http://www.youtube.com/watch?v=1lyu1KKwC74

http://www.youtube.com/watch?v=d020hcWA_Wg

Well guys, I have some very sad news.

All of those pages worked for me without any trouble.

I was even doing downloads at the time.

Something about your system may be blocking you from playing the videos.

I have called for more help. One last thing;

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

I was posting my response when the forum when down yesterday, apologies for the delay.

The vevo channel seems to be the only one that requires the Flash Plugin, other videos on youtube did not require the plugin.

There was another work around I found in Google Groups that suggested clearing the cache would clear the error, but after testing on a few computers I am beginning to think its the vevo channel.