Silverlight and Firefox

On my primary home Windows PC, somewhere along the way, the Microsoft Silverlight plugin stopped functioning with Mozilla Firefox. True, there had been several updates to both Silverlight and Firefox on this computer, since the last time I recall that it worked, but it still worked on my other PCs.  What was different on this one computer?

I was stuck in a loop, where a web site, such as Xbox.com, would tell me to "upgrade to the latest version of Silverlight" in order to view their home page video and yet the Silverlight download page told me it was already installed.  On the Netflix.com web site, when I tried to play a movie, it just took me to a page that said "Thanks for installing". In other words, Silverlight was properly installed and yet it still didn't work with Firefox!

Sad to say, it took me way longer than it should have to figure out the problem. Back at the end of August 2010, Microsoft came out with update KB2264107.  What I had done on this particular computer was to set the Session Manager key CWDIllegalInDllSearch value to 0xFFFFFFFF.  On my other computers, I had set the CWDIllegalInDllSearch value to 2.

One solution would be to change the CWDIllegalInDllSearch value under the Session Manager key, but I wanted to keep it as it was.  Instead, I added "CWDIllegalInDllSearch"=dword:2 under the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\plugin-container.exe key I created.

Actually, first I added a firefox.exe key, but when that didn't work, I immediately recalled the change Mozilla made back in v3.6.4 adding crash protection for third-party plugins.  If dom.ipc.plugins.enabled.npctrl.dll is set to False (or dom.ipc.plugins.enabled is set to False and dom.ipc.plugins.enabled.npctrl.dll is not set to True), then one would need to use the firefox.exe key or else enable crash protection for the Silverlight plugin (npctrl.dll).