If you model the two alternatives as Bernoulli processes with unknown success rates, and assume that the only difference between the two is what is specified on

If you model the two alternatives as Bernoulli processes with unknown success rates, and assume that the only difference between the two is what is specified on the page, and that they don't interact, and you assume a uniform prior on both parameters, B's conversion rate is higher than A's with probability 0.999572.