Is Windows Defender the only Firewall?

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select Network.

[56+] Type about:preferences#general<enter> in the address bar. Look for Network. +++++++++++++++++++++ Look for Configure How Firefox Connects and press the Settings button. If you are using a proxy, make sure those settings are correct. If there is no proxy, first try No Proxy. If there is a problem, then try System Proxy.

Thanks for your reply.

I am no expert, but as far as I know Windows Defender is the only firewall. I use Avast!, but no firewall there.

I followed your advice on "Configure How Firefox Connects". The setting was originally "System Proxy". I changed it to "No Proxy", but the error continues.

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Thanks for that last reply.

I took no further action yesterday, but -magically- firefox works fine today. Noting that I left the computer in sleep mode overnight. I.e. it did not go through a full restart.

Well, whatever. Please flag your last post as Solved Problem so others will know.