What makes the web great is its constant change and innovation. How is it that a 2 person startup can deal with it's users changing browsers whenever they want, but a giant corporation can't? When your browser is beholden to a corporate dev cycle what you get is Internet Explorer.

What exactly would be wrong with a test system that included support for a variety of browsers? Perhaps they could automate this test suite. Any process that made your dev system more agile would be a step forward in this turbulent economy. The current rate of change in the world is going to be increasing exponentially for the foreseeable future. Those well adapted to this environment will prosper those who aren't will perish.

Furthermore, "faced with deciding which is more important: security updates or the critical production web application needed to manufacture your product is not a happy place to be." if you're running the same browser to browse the web and do process control you're asking for XSS/CSRF attacks against your process control system, setup some special link on the desktop that launches a custom browser, then you can keep that browser stable and have an up to date browser for the rest of the internet. Personally, if I was charged with securing a process control system I would have it entirely disconnected from the rest of the corporate network. Only systems that need to access the process control should be connected to that network. We live in the world of stuxnet.