The idea behind this is to make the heavy catpcha misuse by lazy webmasters a bit less unbearable, at a potentially hefty cost to privacy. Which is still appreciable in the rare cases when you use proxies without looking for privacy at the same time.
However, the add-on simply doesn't work. Clicking on "get more passes" just brings me to the add-on's website, which explains various interesting things about the extension but doesn't perform the task I was sent there for (giving me a way to obtain passes).
Edit: okay, it works, but there's a big trick: the "get more passes" feature won't particularly trigger a captcha. So, if the IP you want to unblock is blocked even from receiving catpchas (thanks Google!!) but your normal IP doesn't even trigger a catpcha, then you need to find yet another IP that's in the middle (does trigger catpchas, but isn't blocked from solving them). Then it will work (solving the captcha will give you a bunch of passes, which you can use on your other IP).
It really needs a proper way to manually trigger a catpcha...