Actually, we've been doing that for quite some time on one of the major projects I work on that uses Java applets, for exactly this reason. We usually recommend a recent version of IE, and as a general policy we don't offer any sort of guaranteed support for Firefox or Chrome. Of course we still test on those other browsers routinely and we'll help customers who have problems if we can, but no-one is getting any money back if they break later because of the kinds of changes we're talking about.

The worrying thing for Mozilla should be how many businesses are essentially telling us that they agree and they're moving or already planning to move back to IE as their corporate standard. It's certainly not always because of Java, but choices like rapid update cycles, lack of long-term support, and willingness to drop useful functionality do seem to be generating an increasing amount of hostility from institutional users.