Have you tried going into Options -> Advanced -> Network?

You can check the connection settings.

• Tools > Options > Advanced > Network : Connection > Settings
• https://support.mozilla.org/kb/Options+window+-+Advanced+panel

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can

I have tried to set the proxy settings to No Proxy and Use System Proxy Settings but when I close Firefox and re-open it the proxy settings are re-set automatically as if by magic to Manual Proxy Configuration HTTP Proxy 188.165.85.115 Port 3128 and I get the message on refusing connections.

The problem gets even more complicated. I am running Firefox on a Windows 8.1 PC with three users 1 Admin 2 regular users. Only one of the regular users shows the odd behavior of Connection Settings, the other two work correctly and have been set to Use System Proxy Settings and stay that way.

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

See also:

• http://kb.mozillazine.org/Preferences_not_saved

Thanks cor-el for your reply. In the meantime I have been able to solve the problem: the three users keep their settings synchronized with Firefox Synch. I disconnected all three users from Synch and reconnected them. The problem is gone.