DO NOT DO THIS !
While I'm not pointing finger on the dev who may be honest. This may be or become a scam. And even if it's not, trollbox.fr might get hacked and behave as the hacker want.
Allowing external javascript to run on poloniex website is DANGEROUS.
It could result in the steal of your cookies, buying/selling coins ...
You are right to warn people about this, I am honest indeed and would never do such a thing like stealing cookies or coins, and paid attention to security on trollbox.fr, but the hacking risk can't be zero and cannot be ignored.
Therefore I myself advise people to not use my service using the bookmarklet, but instead to go to trollbox.fr directly.
I'll update the post to include that warning.