This post is a duplicate i made by mistake, please remove one of the posts with the same contente. Thanks.

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

I did try that, it does not work, i also removed firefox, installed again, and changed firewall permissions after that.

But again, it does not work.

Also just tried reinstalling firefox again, this time disabling the firewall in the process before starting up firefox. Did also not work.

Reinstalling Firefox almost never helps, as your settings are stored in a profile which will be reused afterwards.

Since you have set Firefox to use the system proxy settings, first make sure they actually work, or use No proxy instead.

If you happen to run Eset security software, see if this article is of help, even though you see no error message. If you use ZoneAlarm, things may be tricky - see this question. If you use any other security software, including MalwareBytes or similar software, please name it here.

Usually, if Firefox connects when restarting Windows in Safe Mode with networking enabled, this indicates security software to be the culprit. Also try to find the reason for what made "all of a sudden" to be all of a sudden. Did Firefox, Windows, or any other security-related software recently update? Uninstalling and reinstalling security software could also fix it.

I also tried to create a new profile. Dind't solve it.

I'm at work at the moment, so i can't really test while restarting in safety mode, will try to validate that at home, and try to see if any changes to security-related software suffered any update or change.

Thanks a lot for all of your help and ideias, i'll let you know when i have more info about this.

Cheers

Also I am using malwarebytes, but I only installed it after Firefox lost the ability to open web pages.

UPDATE:

So i've changed the proxy configurations on firefox to:

"auto detect network configurations for this network"

Now i am able to access www.youtube.com and www.facebook.com, but other sites like google and pretty much everything else still does not open.

But, if I change the proxy to "Use system proxy configurations", a error is raised when trying to reach www.google.pt, that says:

" The page cannot be displayed

Explanation: There is a problem with the page you are trying to reach and it cannot be displayed.

Error Code: 502 Proxy Error. Forefront TMG denied the specified Uniform Resource Locator (URL). (12202) " "

Please let me know if anyone has any ideias on this, im becoming increasingly confused.

Could it be the proxy itself blocking firefox but not other browsers? I really lack the networking knowledge here to troubleshoot this.

Thanks a lot guys.

The error message indicates your network uses Forefront TMG by Microsoft. This thread (as well as this and this page) shows it may need some additional configuration in order to allow other browsers to work.

Perhaps ask your network administrator what changed recently?