Sorry, I have no direct answer to your question. However, hopefully I may have a solution to the problem you are trying to solve.
Firstly, I don't think VLC plugin for Mozilla is operational at all. Having read a couple of threads here, I re-installed VLC v1.1.5 checking the "mozilla plugin" tickbox in the installation settings window and I could see the VLC Plugin on the list of plugins in my FireFox (Tools->Add-ons->Plugins tab) after that. However, this did not help. Still, clicking on the video-link on the web-page, I am taken to a black page in Mozilla and nothing is going on. Also, no additional plugin files have been added to the Mozilla Firefox plugin folder you are referring to.
Down with plugins. My problem was in not being able to start video automatically from websites. If you are trying to resolve the same, then simply go to "Tools->Optios" in the Firefox and select the Applications tab. You will get the list of content-to-action mappings. Scroll to the group of three entries that mention ".asx" content. Change the action for each of them to 'vlc.exe' by clicking on the current action in each entry and selecting from the drop-down list. If there is no vlc.exe on the list, use the 'use other..' entry at the list's bottom. It worked for me. Now I've got what I wanted: I do not have to copy the shortcut from the webpage and paste it into VLC manually to watch a clip.
Yes, it takes some effort to make stuff work
I am not good at this generally, so I may fail to help if it does not work for you but will definitely give it a try.
Good luck!