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Crash signatures ( what's this? ): RtlFreeHeap
This is a generic crash signature that can have a number of causes.
One of the most common causes that we've identified is malicious software (a virus) called TR/Agent.70656.13
One of the resources below may be able to help remove this virus:
You can also try general troubleshooting steps at Firefox crashes - Troubleshoot, prevent and get help fixing crashes.