According to this stackoverflow answer:

This happens when the page itself defines a global variable called console, for example. If the page is browser-sniffing to decide whether to define it, the behavior could differ in different browsers.

Which is what happens in corestup.js, lines [4,13]:

var console;
if (!console) {
    // Even IE9 only exposes console object if debug window opened
    console = {};
    ('log error debug info warn assert clear dir dirxml trace group'
        + ' groupCollapsed groupEnd time timeEnd profile profileEnd count'
        + ' exception').split(/\s+/).forEach(function(property) {
            console[property] = _.identity;
    });
}

I've submitted this as an issue: https://github.com/odoo/odoo/issues/903