It taken much long time for Mozilla to release Firefox 3.6.4 final with crash protection feature Mozilla now released Firefox 3.6.6 which terminates unresponsive plugins after 45 seconds which was 10 seconds in case of Firefox 3.6.4.
Mozilla released Firefox 3.6.4 with crash protection feature which allows uninterrupted browsing for Windows and Linux users when a plug-in like Adobe Flash, Silverlight, Apple Quicktime crashes or hangs user can reload the page to restart the plug-in again and start browsing.Here Firefox terminates unresponsive plugins after waiting for 10 seconds.
Mozilla got feedback from Firefox 3.6.4 users using older computers that for playing games can expect longer periods of non-responsiveness from plugins , for this reason Mozilla extended the amount time of Firefox has to wait before terminating non-responsive plugins from 10 to 45 seconds.This change has been made in Firefox 3.6.6 which released as automatic update for all users.
You can read Firefox 3.6.6 release notes for more details.