Just adding my two cents here. I had a similar issue I think. Quicktime would not load in any browser.
I am in a multi-user Windows 7 domain environment. My users are not administrators on the Public/Lab machines. I create the default user profile from the administrator account and the users account is created from this.
So to the problem and solution...
Every user had in their registry path "HKCU\Software\Apple Computer, Inc.\Quicktime\LocalUserPreferences" the following...
Keyname: Folderpath
Key Data: C:\Users\Administrator\AppData\LocalLow\Apple Computer\QuickTime\
Well that's not very useful if the user is not an administrator...they have no rights to see that folder and therefore Quicktime add-ins would fail to load.
So I tried to just use group policy and change the data in the key to use the proper wildcard of %username% in place of administrator but Quicktime did not seem to like that and it failed.
I resolved the issue by writing a VBscipt that replaces the username in the key with the current logged in user. I have this set to run at logon using group policy. I assume you could place this in the startup folder.
Take the following, add it to a text file and rename it with the extension .vbs. Then run it. Works for me. If this isn't a bug with Quicktime, I don't know what is...
Copy everything below, not this line that you are reading...
'The following script will find out the account name of the current
'logged in user and pass that as a variable to alter the registry key
'listed in line 17
On Error Resume Next
Set wshShell = WScript.CreateObject( "WScript.Shell" )
strUserName = wshShell.ExpandEnvironmentStrings( "%USERNAME%" )
Username=strUserName
'Uncomment line 5 to see what username you are getting as a test
'WScript.Echo Username
const HKEY_CURRENT_USER = &H80000001
strComputer = "."
Set StdOut = WScript.StdOut
Set oReg=GetObject("winmgmts:{impersonationLevel=impersonate}!\\" &_
strComputer & "\root\default:StdRegProv")
strKeyPath = "Software\Apple Computer, Inc.\Quicktime\LocalUserPreferences"
strValueName = "FolderPath"
strValue = "C:\Users\" & Username & "\AppData\LocalLow\Apple Computer\QuickTime\"
oReg.SetStringValue HKEY_CURRENT_USER,strKeyPath,strValueName,strValue