This action by Mozilla raises awareness of the fact that Java security updates are too slow and too opaque and it's time to change to something else.
It also raises awareness of the fact that you can't trust some of the big names in the browser industry not to break stuff every few weeks just because they don't like it and then push the changes on you whether you want them or not.
Introducing restrictions so tight that you can't actually do your useful work any more isn't security, it's just broken.
That's a nice theory, but Mozilla's idea of "long term" support is still forcing an upgrade more than once a year just to maintain security patches, and with only a 12-week overlap between a new version starting testing and the complete end of support for the previous version.
That sounds like a long time if you're reading this in Firefox on your home PC, but if you're responsible for a large corporate network with thousands of users and a hundred critical intranet applications to keep working, many of which have a measurable dollar amount attached for every hour of downtime, different rules apply.
There is a reason so many large organisations stuck with IE6 for so long: having tried and tested, stable software is far more valuable in that kind of environment than having the latest shiny features that none of the in-house applications you're actually providing the computers/browsers to use need anyway.
It also raises awareness of the fact that you can't trust some of the big names in the browser industry not to break stuff every few weeks just because they don't like it and then push the changes on you whether you want them or not.
Introducing restrictions so tight that you can't actually do your useful work any more isn't security, it's just broken.