There have been a few bugs where suggestions have been made to provide a way to disable the developer tools and they have all been WONTFIXed.
I would like to strongly suggest that there be kill switches for the developer tools, for two main cases.
1. Kiosks: It's important in kiosks that users not accidentally bring up things with keystrokes. The developer tools involve so many keystrokes, it's quite easy to accidentally bring them up.
2. Enterprise/Govt/etc.: These are cases where people simply don't need the developer tools. There should be a way to disable them.
Note that despite comments to the contrary, Chrome and IE DO provide a way to disable the developer tools via group policy:
Chrome:
http://www.chromium.org/administrators/policy-list-3#DeveloperToolsDisabled
IE:
http://technet.microsoft.com/en-us/library/cc985351.aspx
Developer Tools Turn off Developer Tools User, Machine Windows Components\Internet Explorer\Toolbars
The reason this is more of a problem now is that the developer tools are no longer XUL overlays, making it much more painful to simply disable them.
The fact is that most of the kill switches preferences work in the build today. We should make sure they stay there and simply fix the two that don't work (scratchpad and responsiveUI).