Fantastic Rated 5 out of 5 stars
Does exactly what it says on the tin. Works very well too.
I have 40 or so personas and have used this add-on to rotate them every 15 minutes. This is also made much more interesting by the fact that personas are synced with FF sync too, meaning when I get home from work, my machine uses the last synced persona - cool! This may not be to everyone's taste (and is not the add-on devs fault, as it is a core feature of FF sync), so a workaround to stop this can be found here:
One improvement I can think of, again - probably nothing the add-on dev can do as it is the way FF loads the personas, is to pre-load the images used in the next persona so that the transition can be a smoother; currently FF swaps persona and then loads the images, making the transition (flicker?) more noticeable than it needs to be.
One last improvement is to make the add-on 'restartless' if possible, as personas don't require a restart - it would make it just that little bit more elegant.
All in all, Good job.