Firefox started blocking Java plugins in January '13. I wonder how long before other browsers follow suit.
If you happen to have the newest Java version which hasn't been publicly announced as exploitable, it will not be blocked unless you enable `plugins.click_to_play` in `about:config`.
Anyway it's still a very good move from Mozilla side to minimize the risks.
IMO all browsers should implement 'click to run' by default for all plugins on all sites