Did you check your security 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.

You can try to reset (power off/on) the router.

See also:

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

Thank you for your answer.

Security software I have under controll (I hope). It does not work even when I switched off the security programs.

Thanks for the link, I tried it even before I wrote here. I'm confused by IE. Both programs behave similarly. Error must be in the OS.

Now I started window in save mode. It work well. Can you tell me, please, how can I find a program that is in conflict with FF? I do not know how. Thank you...

It is possible that you only disabled the user interface of your security software and that the services were still working in the background.

You can use the MSConfig program or the Autoruns utility to see which software and services are getting started (be cautious with disabling services).

• http://technet.microsoft.com/en-us/sysinternals/bb963902.aspx

Thanks for the advice. I know both programs. I have already thought out method of finding errors. Perhaps :-)

I'll try it until the weekend. I will write the result.

It works now normally. "Windows 8.1 update" KB2901549 corrected the error. Bug was in IE11.