First, I am not sure why there are two installs of Flash in the extensions section of the troubleshooting information, but if there are two, please uninstall the previous version.

Second, I have seen this when there is a default virus scanner/antivirus, but this was taken out of Firefox over a year ago? does not matter. What matters is that you might be running into an issue with a feature of your antivirus. Then try these steps if disabling add ons and antivirus does not resolve this:

• What to do if you can't download or save files

It is possible that security (Anti-Virus, firewall) is causing problems. Try to disable security software temporarily to see if that makes a difference.

Thank you for the reply. I fixed the problem days ago by deleting a folder or folder in the user data. Don't remember now which one but it worked out. :)