Some sites can freeze the TLSA Validator core
Sites that freeze the TLSA Validator: https://www.devk.de/kundenservice/kfzservice/index.jsp
This freezes the extension every time. Running Version 2.1.1 on Firefox 30 running on Windows 7 64bit.
Dig result: dig TYPE52 _443._tcp.www.devk.de return SERVFAIL or "connection timed out; no servers could be reached".
Notification
This issue was reported for the NPAPI-based extension. Plugin cores are based on js-ctypes now. Unfortunately, the js-ctypes-based extension can also be affected when running in synchronous mode. This mode is not default. The default is asynchronous validation of both plugins. Issue will be closed.