Yes, you are right. Here's the relevant documentation from Mozilla.
"Extensions that are installed this way include the Java Quick Starter extension for Firefox (see above), the Microsoft .NET Framework Assistant [13] [14] the RealPlayer Browser Record Plugin extension, [15] and the Lenovo ThinkVantage Password Manager extension for Firefox [16] [17]. Although you can disable the extension in the Add-ons manager, the Uninstall option may not be functional (it will be "greyed out). In such cases, experienced users can uninstall the extension by removing the associated Registry entry and/or the contents of the folder containing the extension; otherwise, simply disable it."
http://kb.mozillazine.org/Uninstalling_add-ons#Windows_Regis...
Microsoft has an article about how to remove this extension:
http://support.microsoft.com/kb/963707/
From the same KB article,
"In Windows 7 and in a forthcoming update for the .NET Framework 3.5 SP1, the .NET Framework Assistant will be installed on a per-user basis. As a result, the Uninstall button will be functional in the Firefox Add-ons menu."
I am using Windows 7 right now and I can verify that I do see that Uninstall button is functional.
http://imgur.com/gX5c8.png
BTW, this just goes to show the kind of reputation Microsoft has achieved in the marketplace. When the uninstall button was disabled, no one thought that it could be problem in the way Firefox works. Everyone (including me) just assumed that it was Microsoft who is deliberately doing this. I don't know how can they possibly fix their image.
"Extensions that are installed this way include the Java Quick Starter extension for Firefox (see above), the Microsoft .NET Framework Assistant [13] [14] the RealPlayer Browser Record Plugin extension, [15] and the Lenovo ThinkVantage Password Manager extension for Firefox [16] [17]. Although you can disable the extension in the Add-ons manager, the Uninstall option may not be functional (it will be "greyed out). In such cases, experienced users can uninstall the extension by removing the associated Registry entry and/or the contents of the folder containing the extension; otherwise, simply disable it."
http://kb.mozillazine.org/Uninstalling_add-ons#Windows_Regis...
Microsoft has an article about how to remove this extension:
http://support.microsoft.com/kb/963707/
From the same KB article,
"In Windows 7 and in a forthcoming update for the .NET Framework 3.5 SP1, the .NET Framework Assistant will be installed on a per-user basis. As a result, the Uninstall button will be functional in the Firefox Add-ons menu."
I am using Windows 7 right now and I can verify that I do see that Uninstall button is functional.
http://imgur.com/gX5c8.png
BTW, this just goes to show the kind of reputation Microsoft has achieved in the marketplace. When the uninstall button was disabled, no one thought that it could be problem in the way Firefox works. Everyone (including me) just assumed that it was Microsoft who is deliberately doing this. I don't know how can they possibly fix their image.