hello demoyamary, your useragent (the information the browser sends to websites to identify its version) - apparently mistakenly - shows you're on firefox version 3.6. probably some sort of toolbar or adware has overwritten it. please refer to this article in order to reset the user-agent settings in firefox: How to reset the default user agent on Firefox

Try to read How to reset the default user agent on Firefox

After following those directions, try to read Update Firefox to the latest release to double check you are using Firefox 17.0.1 or later