It could be some form of malware on your PC. In the past I have encountered malicious software doing something similar, preventing healthy connections. Now, I am not saying that is the issue, but it could be, you can try the following and see if it helps you solve the issue: 1. Check your browser for any add-ons or extensions you do not recognize and remove them. 2. Check your installed programs and see if there isn't anything suspicious that was installed lately (If there is, simply remove them). 3. Install any popular antivirus and do a quick scan (Majority of the providers do have free versions of their software). Or just use Windows Defender. It works really well in most cases. 4. Install and scan your PC with Malwarebytes and Hitman Pro to clean most adware. 5. Fully uninstall and reinstall Firefox. After this, in most cases, the issues of malware should be solved. If there were any in the first place. Let me know if this helps!