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Strange TLS problem with browsers

I have to help a user with a desktop PC, Windows 7 (unknown edition, probably HOME). Internet connection is wireless to some cable modem access point. Uses Avira for system protection.

Recently, he played some online game, which got slower and slower and finally broke. Subsequently, web access with Firefox, Internet Explorer and Chrome failed. When trying to access google.de, Firefox needs a long time trying to connect, then fails with a message that "The server refused the connection because the client fell back to a TLS version lower than required by the server [SSL error inappropriate fallback alert]". I don't know what IE and chome tell, but they seem to be blocked either.

Internet connection itself seems to be OK ... a ping to www.microsoft.com works flawless.

Other sites than google (i.e. www.gmx.net) seem to fail, too. Remarkably, when trying to access google.de and gmx.net the user didn't enter the https:// prefix ....

I understand that error message, which might be partly caused by the retirement of SSLV3. But why does it happen with non-https requests, why does it happen without the user changing any settings, and how could that be fixed ?

Additional I'm unfortunately restricted to phone communication ... so I need some easy directions for fixing it ...
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Fixer of Problems
Most Valuable Expert 2014
Google redirects to 'https' these days even if you put in 'http'.  www.gmx.net may do that after a login.  Internet Explorer and Chrome both use the Windows Certificate store but Firefox has it's own.  And ping checks only the most basic level of network connection.  It does not check 'http' at all.

The error message sounds like Firefox needs to be updated to the latest version.

By the way: I did the PING for exactly that reason - to rule out a basic network breakdown, WiFi problems, etc.
Dave BaldwinFixer of Problems
Most Valuable Expert 2014

You're welcome!