How do I make a plugin local to the firefox directory

I use a portable Firefox when I move around the several computer labs on my campus. It is a convenient way for me to keep my browsing history and extensions across computers.

The problem comes with plugins, each computer lab has its own different outdated plugins which firefox defaults too. I have too disable plugins because its such a bad security flaw, and outdated plugins cause crashes.

How can I make Firefox select plugins only from the directorys that I choose?