Using two browsers in this manner does have security
benets. For example, consider the case of re
ected cross-site
scripting (XSS). In a re
ected XSS attack, the attacker crafts
a malicious URL containing an attack string and navigates
the user's browser to that URL, tricking the honest web site
into echoing back the attack string in a dangerous context.
The attack has more diculty succeeding if the user runs
more than one browser because the attack relies on which of
the user's browsers the attacker navigates. If the attacker
navigates the user's non-sensitive browser to a maliciously
crafted URL on the user's bank, the attack will have no
access to the user's banking-related state, which resides in
another browser.
From this discussion, one might conclude that isolation
of credentials and other state is the essential property that
makes using two browsers more secure. However, another
security property provided by using multiple browsers is
equally important: entry-point restriction. To illustrate
entry-point restriction by its absence, imagine if the attacker
could arbitrarily coordinate navigation of the users' two
browsers and open an arbitrary bank URL in the sensitive