Comment # 37 on bug 1184817 from Takashi Iwai

If the system is screwed up by the enablement of an Ethernet device, the
possible cause is either too many (unhandled / handled) wild interrupts or
memory corruption or such bug.  Usually the latter should be visible in the
kernel log as a kernel crash, while the former isn't always seen -- especially
if the irq table is already suspicious (the dead irq 9 was reported).  If the
interrupts go crazy, everything can happen, no matter which I/O.

The fact that web browser doesn't open implies that something is blocked, and
it could be a network.  I have no grasp how many bugs you already submitted and
all smell really like the same cause.

When the problem happens, and when you unplug the USB Ethernet device (instead
of power-off / reset), does the problem persist?