While this may not help you, there are certainly options
for deploying silently without the MSI if you're so inclined.
If you really can't deploy anything but MSIs, then how do you handle the other thousands of installers that aren't MSI packaged? Firefox seems like a nit in comparison to the legions of corporate-important applications that use any other install method but MSI. Or legacy apps that were packaged before the popularity of MSI. Or in house desktop applications. Or any number of other obnoxious speed bumps you deal with when managing a large number of desktops + app deployment in a corporate environment.