What does the NPLastPass/LastPass plugin in Firefox do?
NPLastPass/LastPass plugin refers to NPAPI, the binary component found in Chrome, Opera, Safari and Maxthon. It will appear in Firefox/Chrome if you have binary installed on any of these other platforms or have installed LastPass using the Universal Installer. Even if you excluded Firefox/Chrome when installing using the Universal Installer, you will still see it.
Even though Firefox does not use this plugin, Firefox detects it on your computer and adds it to their plugin list.