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Firefox with TLS 1.3 enabled crashes IIS10

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We're testing a website on Windows Server 2016 TP4 (IIS 10). The web site uses SSL and frames. When we access the site with Firefox 40 or higher, multiple IIS Worker Processes start running using large amounts of CPU time. Other browser accesses then fail with 500 errors. If we kill the long running Worker Processes, normal operation is restored. If we go into about:config and change SECURITY_TLS_VERSION_MAX from 3 to 2, the problem goes away. Appears that this option changes the max TLS version from 1.3 to 1.2. Is there any fix for this behavior?

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This forum is for Firefox end user support. Please see this KB article.