With the latest / since Firefox 3.6.4 plugins are run in their own process. That’s great news because it will help to gain more stability. And it opens a lot of new possibilities. For example you can create your own plugin process loader *gg*.
I wanted to remove the plugin loader binary (plugin-container.exe on windows in the Firefox program directory) but only removing it (or replacing it with a same-named directory) did not work. Then I replaced it with a exe file which just does nothing. But this does not work at all, Firefox freezes in all these three scenarios.
Looks to me that this Gecko OOPP feature isn’t properly implemented in Firefox. It only handles the case that this process crashes but it can not deal with the case there is nothing to start?
Update 2: My Bugreport is a duplicate of Bug 535077 (Failing to exec() mozilla-runtime (plugin-runtime) for a sync launch causes Gecko to hang) which contains more information on the topic.