I finally jailbroke my iPhone. But although the process was supposed to be straightforward with QuickPwn, but it wasn’t.
First try, error while in DFU mode. Next try, the firmware was properly installed, but the iPhone froze on the pineapple logo.
Reboot, reboot, reboot, no way to get anything else.
I was able to restart the jailbreak process a few times, but always without getting past the pinapple logo.
During the process, iTunes was annoying. It constantly wanted to run in order to mount the iPhone. I first let it go. On the next tries, I closed it as soon as it raised. But nevertheless, the iPhone remained bricked.
At this point, I restored the original firmware.
Last try: I fed up with iTunes messing up the QuickPwn process and I just blocked it:
chmod 0 /Applications/iTunes.app
Then, guess why… QuickPwn worked peacefully and the jailbroken iPhone properly rebooted and now works like a charm.
Of course, iTunes was allowed to run again afterwards:
chmod 755 /Applications/iTunes.app
This workaround is ugly, but well… The point is: it works.