Firefox occasionally suggests that a "Refresh" might improve performance. We had a naive user press that button and wipe out a significant amount of customisation. Part of what resulted is that the master password option was turned on by the refresh, even though the user had not set a master password and had never enabled that feature. Of course, there being no master password it was impossible to turn the master password option off. We fixed this by running the password reset thing: chrome://pippki/content/resetpassword.xhtml but researching this was a considerable time waster.
We also had to reinstall their addons along with all the company PKI certificates. Their previous profile being saved to their desktop notwithstanding.
These sort of user bombs are about as unfriendly a UI as I can imagine.
In any case, how does one turn off that particular annoyance so that the unwary are not led to do something they really, really would not chose to do if they knew what it did.
