I'm pretty sure this happens with many versions earlier than 5.1.0 RC2 such as 5.0.2 and even the latest 5.1.1 from GIT, but I only have RC2 and Beta 1 on hand to provide an example with.

What happens is that a few sites such as Twitch.TV will immediately crash the QT application with error:

fontEngine: Can't change family name of font
fontEngine: Can't change family name of font
ASSERTION FAILED: !callFrame->hadException()
interpreter\Interpreter.cpp(998) : JSC::JSValue JSC::Interpreter::executeCall(JSC::CallFrame*, JSC::JSObject*, JSC::CallType, const JSC::CallData&, JSC::JSValue, const JSC::ArgList&)
(Internal error: pc 0x3e5 in read in psymtab, but not in symtab.)
(Internal error: pc 0x3e5 in read in psymtab, but not in symtab.)
(Internal error: pc 0x3e5 in read in psymtab, but not in symtab.)

To my understanding this is some sort of font issue with the javascript engine.