stop FF 3.6 from looking in the local machine for add-ons

I'm on FF 3.6.27 portable and I'm trying to stop FF from looking in the local machine for add-ons, on my home PC I'm getting DivX, .net and java quick starter, but there is no telling what stuff will be on other peoples systems, I'd rather FF just didn't look and only looked into its own add-on folder in the USB drive..

I noticed the other thread about this issue, but "extensions.autoDisableScopes" doesn't seem to be a part of 3.6 so i can't change that. I obviously can't change the registry setting on every PC i plug this USB into so i need a fix for FF.

any help or suggestion would be very welcome