Nope its, perfectly good when you're firewalled to fuck, just like any other web browser
It gets a bad rep as a large percentage of the worlds morons are using it, besides its odd vulnerability that microsoft patch up within a couple of days.
Apple just had to plug 50 holes in its latest update for safari (3% of the browser market), so if you're using that thinking you're somehow safe from any incoming attacks then think again. Similarly, last year Mozilla recorded 99 vulnerabilities, which is the highest amount ever recorded for any browser to date. As we see Firefox near toward a 50% market share, I expect to see it becoming a hot target alongside IE.
People have to remember that none of these browsers are safe, if you're a good hacker you'll get through any WAN facing app, just don't get fooled by the anti-MS stuff, they get the wrap for a plethora of obvious reasons
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