Microsoft .NET Framework Extension

Hello and may the year 2015 continue better for everyone than it has started.

I come once again to seek your help.

Here’s what I have on my computer:

ADD AND REMOVE PROGRAMS
Microsoft .NET Framework 1.0 security update (KB2742607)
Microsoft .NET Framework 1.0 security update (KB2833951)
Microsoft .NET Framework 1.0 security update (KB2904878)
Microsoft .NET Framework 1.1
Microsoft .NET Framework 1.1 French language pack size 3.04MB
Microsoft .NET Framework 2.0 Service Pack 2 size 184.00MB
Microsoft .NET Framework 3.0 Service Pack 2 size 240.00MB
Microsoft .NET Framework 3.5 SP1 size 28.07MB
Microsoft .NET Framework 4 Client Profile size 117.00MB

FIREFOX EXTENSION
Microsoft .NET Framework 0.0.0.

AVAST reports:
Your browsers seem to have plugins of bad reputation.
They recommend removing the Microsoft .NET Framework 0.0.0 extension.

I have read many articles on how this works and elsewhere advising against uninstalling Microsoft .NET Framework

What should I do with all this Microsoft .NET Framework???

Thank you in advance for your advice and have a very windy day...