Please reinstall Firefox by downloading it again from mozilla.org. Something in your install is broken. Good luck and please report back here to let us know if the problem is solved!

You may need to delete the Firefox program folder (C:\Program Files\Mozilla Firefox\) manually in case you have other (security) software that is using or protecting files and preventing Firefox from updating all files.

I have reinstalled it 2 times with complete delete of the folder manually! I have also installed the java runtime new version 7. But no resolve of the problem.

It has worked always until yesterday. My security program has never make any problems with mozilla. I guess the problem comes from JAVA. In the past i had a similar problem but cant remeber how i resolved the problem.

see if this is helpful : Unblocking the Java plugin

thank you

I´ve found the error. My Security Software "Avast Internet Security 2012" blocked the Java Plugin. Mozilla only work in the "Sandbox Mode". I hope it helps other people to solve the problem. Always when installing or reinstalling software you should check also your security software.