FF with upcoming click-to-play feature is available at:
   http://www.mozilla.org/en-US/firefox/channel/#aurora/aurora-desktop
this is being versioned as 14.

Install JRE 6u32.

To test it without affecting your existing Firefox profile etc., go to the Aurora install directory on the command line and start it e.g. with:
  firefox.exe -P Minefield -no-remote
To enable click-to-play, go to about:config and set plugins.click_to_play to true, restart Firefox.

Load the attached javatest.html testcase which contains an empty applet.

Problem is reproduced if you see FF hangs.