Ronald van den Heetkamp has claimed that he found a vulnerability that affects all released versions of Firefox, and so the Mozilla security group and others have been investigating it, as we do all such claims.
In this case, it appears to me as though Ronald is simply mistaken. The files to which Ronald demonstrates access do not have the user’s settings, though he claims otherwise. Those files (the user’s data) are not stored in the Program Files hierarchy on Windows, or the equivalent on other operating systems. Instead, the preference files that he is showing in his “exploit” are ones that are defaults that are shipped with Firefox, and made freely available on the web. Again, these are not user settings, but defaults that are shipped with all copies of Firefox and contain no personal information.
(NB: this issue should not be confused with the recent “flat chrome” directory traversal vulnerability that affected users of some extensions, and which 184.108.40.206 fixes.)
I don’t know if Ronald will issue an update to his post, as he did for a previous mistaken vulnerability report, but since the story has been taken at face value by Slashdot and likely others, I thought I’d post about it here.
Edit: this is the same thing that RSnake and others on his blog discussed last May; comments there are possibly of interest. Ronald participated in the thread but didn’t think it was an important problem back then, if I understand his comment correctly.