When Mozilla said, "Enterprise has never been--and I'll argue, shouldn't be--a focus of ours" I was shocked that they publicly stated that, but not surprised that is their stance.
Internet Explorer (IE) is easily the defacto web browser in the business and likely will be for some time. Microsoft owns that space pretty handily. Yes, there are those small companies that have migrated successfully to Firefox or Chrome or others, but they are the exception, not the rule. We are talking Enterprise. These are the companies with thousands of employees with many custom or customized internal applications. These applications don't get updated quickly. It can take months or even years to upgrade to new versions. Even patches have to be rigorously tested and QAed before being rolled out. Especially if those apps are mission critical.
For Mozilla to say that Firefox isn't designed with the Enterprise in mind gives them the ability to remain flexible and aggressive with their development strategies. Enterprise's need and are large enough typically to demand long term development cycles, so they can plan accordingly. Sometimes Enterprise-time and Internet-time are not compatible. For Mozilla to focus on Internet-time is probably wise from their development strategy, but I think it can be easily argued that perhaps they shouldn't have made the statement they did.
Enterprise IT not only wants to keep things standardized but often NEEDS to. When you are supporting thousands of PCs, supporting multiple web browsers, with multiple versions, with different plug-ins would be a nightmare. Supporting IE, especially a single version, simplifies support. Errors and bugs can be managed. Application customizations can be handled. From the IT perspective, the more everyone's PCs are the same, the easier it is to support them and deploy fixes/patches equally throughout the enterprise.
Even IE isn't immune from being rolled out slowly. My company is currently on IE8, which is probably better than some companies, but IE9 just came out and we are not compatible with it yet. Patches are coming to fix that, but this is something that Enterprises have to deal with. When it's one browser, it can be managed. When it's multiple browsers, it becomes a lot less manageable, especially when they have radically different release time frames.
Mozilla just began a more aggressive release schedule. Chrome has always been very aggressive. Enterprise IT departments can't keep up, so they standardize on one (normally IE).
Standardization is a word that could change this, in time. For a long time Internet Explorer, because of it's market dominance, included a lot of Microsoft-only code that rendered websites a very particular way or included scripting/tools that were unique to Internet Explorer. Because of the dominance of IE Enterprise software companies and the Enterprises themselves coded their applications for Internet Explorer. A lot of that code still exists. Enterprises don't just change things because the Internet says it's obsolete. There has to be a business case for making the change. In the case of our company, the software we use has an external customer component. IT can dictate what we use internally, but they cannot control the customer, so we have to keep on top of these changes as best we can. IE isn't always the browser of choice any more.
IE has lost the dominance it once had in the market, as a whole. It's still very important, but it no longer commands 90% of the market. Microsoft has since started making Internet Explorer much more standards (web standards) compliant. As has it's competition, Mozilla and Google. They are all trying to one-up one another in becoming the most HTML5 compliant as possible. The HTML rendering engines, for the most part, are what make the various browsers behave differently when rendering a web page.
With all the web browsers moving towards HTML5, could we finally get to a point where it wouldn't matter which web browser you used? I think we are a few years, at best, for that happening. Outside the Enterprise I believe this reality is much closer, but in the Enterprise it simply takes businesses a lot longer to migrate to the cutting edge technology. Their focus is on their customers, not on their internal staff. There are still lots of companies running Windows XP. Internet Explorer 9 won't run on Windows XP, so those companies will have to do major, and expensive, upgrades before they can change their web browsers. Most will wait until they absolutely HAVE to. It's just the nature of the Enterprise.