Interesting, if you take a look at its source-code you'll notice what this add-on does is quite trivial, it merely reads a single Firefox preference option (containing the installed themes) and shuffles the contents.
Hence, i'd say whatever is happening is isolated to your system in case you want to investigate further (nobody else reporting such an issue) -- Hm, or perhaps you have installed way too many themes?
I can't say anything more positive that wasn't already said by others. The only thing I'll add is that while it does throw up different personas, it only seems to throw up the same 9 or 10. If I use firefox 20 times, the same 2 or 3 personas will show up at least 12 of those times with a few less-used ones sprinkled in for the other eight. There are a lot of other personas I installed that have never come up, ever.
It's the best addon for personas to me, cos change only with the personas what i have, and not all personas fit with my buttons and configuration color. For now only change on start or restart, missing button for change without restart.