I am the developer of FoxyProxy. Some users have requested that it work with PortableFirefox. I haven't used Portable Firefox yet, but I'd like to know what generally needs to be changed to make an extension work with PFF.
FoxyProxy has a settings file which, by default, is created and stored in the user's profile (this can be changed, however).
Thanks for any tips,
p.s. is there anyway to subscribe to this thread so I get email notifications? I'm not familiar enough with Drupal