Looking at my responses to my previous post, it seems pretty clear that a lot of people simply don't understand why companies stay on old technology. I have some other thoughts I'd like to give on Mozilla and enterprise, but before I do that, let's talk about the why.
Imagine that you needed a custom web application developed for your company (not a technology company). You would design the solution and build it based on the current technology. You would attempt to anticipate what the future looks like, but things change and you built this based on what you thought was the correct technology. (Remember, this was a couple years ago.) You would build the app and deploy it, and then you would probably move the team on to other things. You might keep one person was kept around, but they only work part time maintaining the app. Over time the app becomes an integral part of your business.
One day a new browser is released and you realize that your app doesn't work with the new browser. Now you have a choice. You can either rewrite the application or use an older browser. Rewriting the app might cost a million dollars. Sticking with an old browser might cost one hundred thousand dollars in support costs per year. Which do you pick?
Update based on a great comment from Wladimir Palant: Or maybe it's that it would be expensive to guarantee the app runs correctly on the latest web browser. Or maybe your app depends on a Firefox add-on that isn't working.
Remember, you're not a technology company. You use technology to run your business. And the job of your technology is to improve your bottom line year to year. So when you make technology decisions, they need to either make money or cause other parts of the business to make money.
Our goal here is to make a profitable business. So you choose to stay with the old technology as long as you possibly can, probably putting off the inevitable, but at least it's saving you money in the short term.
What you need to take from this:
Businesses do not make technology decisions independent of their financial impact!
This is why products like Browsium exist. You may look at a it and say "It seems expensive?" It's actually not expensive at all when you compare it to the larger costs of rewriting your application.
And this doesn't just happen with custom applications. Maybe you bought a particular app from a company that went out of business. Or you bought it at a particular version that only supports a particular browser.
These are the realities of running a business. Technology decisions are never independent of financial decisions.