Not that simple...
Actually, it wouldn't be.
Right, a lot of firefox fans evidently have never worked in a large environment. There is nothing wrong with that, but you simply don't understand the issues we have. An enterprise environment is not the same as your home PC where if something breaks then you just figure out what's wrong and then get around to fixing it later.
In an enterprise environment, if you roll out a new browser with no testing and stop just 5000 users working for a morning (3 hours) while you figure out what the problem is and then fix it you have cost the company 15000 working hours in lost productivity. To put that another way, it's 1875 (8 hour) working days or dammed near 7.5 man *years*. If you cause that, then sorry your going to be out of a job. It is expected that when you roll something out that it actually works first time, with no issues.
That is why we test things first. It's not just for the fun of it, and it's not just a case of opening up an app and saying "yep, this works!"
I have seen a standards compliant apparently "working" app that visually completed testing. However, the user then came back a day later and said that she hadn't received the confirmation email, checking with the provider showed they hadn't logged the order. In other words, the app silently failed. In those situations you can't upgrade the desktop estate of browsers until the app is fixed. That particular web app wasn't even ours or supported/supportable by us, yet it was mission critical to the business. Hence, we report it to the people that support it and continue testing everything.
The people supporting it also have other work to do, and upgrading a web app to support a new browser tends to get put in a que behind all the other work they have been given to do. It may well take weeks or months until they get around to supporting their app. Until they do, you simply have to stay with an older version of the browser.
This is the problem with Mozilla dropping support for a new browser *instantly*. Even if IT is willing to drop *everything* for every single new FireFox release then your still looking at a week to discover all of the problems with existing apps, and then however long it takes the (often 3rd party) developers to actually fix any problems discovered.
Until that time, your stuck on an older version with no support, vulnerable to known bugs otherwise known as exploitable security flaws. I take it you see the problem? This is why Enterprises simply can't use Mozilla apps in the enterprise, though every single tech in the IT department uses them at home. Then you have the side effects. The users use IE at work, and... what do you think they use at home? IE probably. If they were using FireFox at work, and found it better than IE at home, then don't you think they might consider switching at home?
Of course, enterprises are evil and don't deserve support. Ah, you just lost those users twice, btw. Once for their work installs, and once for lost home installs. They'll just stay on "The Internet" at home, having never heard of a browser or being interested in learning what it is.
Is supporting an old release for 6 months or so THAT hard? Yes? Ok, we'll have to stick with IE then. No, we don't want to. However, Mozilla leave us with no alternative.
See the problem? And no, we can't support Firefox ourselves FFS. Even if we had the developers time we don't have access to the top secret vulnerability reports submitted to Mozilla so we don't know what to fix until zero day exploits are in the wild. No thanks!