Overall, FIREFOX seems to be the browser with the least number of vulnerabilities. There was a major issue a few weeks back, as discovered by Firefox. An immediate fix was issued. Firefox's "Automatic Update" function ensures all Security Updates get to users as fast as possible.
IE has far more vulnerabilities, owing perhaps to the fact that more people use it. Most updates are available only on the Second Tuesday of the Month (including Critical Updates), except when the updates are deemed to be extremely critical. IE's Automatic Update feature should also be turned ON.
Firefox code is not as robust as IE's, so it loads faster.
Addons as recommended by Mozilla and Microsoft should be the only ones used for their browsers to avoid problems.
