Unresponsive hardware, ethernet shutting off and kernel panic sounds to me like a kernel bug. Might not be, but it's hard to tell without more information.
@ratt: does this happen with any other browsers? It's important to know if it happens with all browsers or just firefox.
You should also try running firefox from the terminal so any errors thrown will display (potentially) useful information.
@both: what kernel version are you running? If you're unsure, open a terminal and type in:
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