Firefox 3.6.6 modifies the crash protection feature to increase the amount of time that plugins are allowed to be non-responsive before being terminated.
Please see the complete list of changes in this version. You may also be interested in the Firefox 3.6.4 release notes for a list of changes in the previous version.
This change was made to allow the crash-protection-feature to be more tolerant of "hang times" in Flash Player; see http://support.mozilla.com/en-US/kb/The+Adobe+Flash+plugin+has+crashed?s=plugin+timeout&as=s
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