Welcome to the forum, @mouse1!
Unfortunately, it is very difficult to know what is going wrong from your description. Where did you get this "1394 camera" plugin? I could not find it immediately with some quick web searches. Who wrote that plugin? Is it open source? Supported by the authors?
Without any support from an active development team, you are very likely out of luck.
Can you reinstall OS X 10.11? For these kinds of legacy unsupported systems, it is very important not to mess with them (e.g., upgrade ) when things are still working, for reasons like this.
Did you check whether Micro-Manager supports your camera?