There is a slight difference between a monopoly and a dominant market position. The latter is only achieved by consistently being better than competitors and it is easy to lose once this is no longer the case. Google with all its current power is not in the position to dictate what all the browsers should do - and prohibiting Firefox from its servers is a) an evil move that would make people reconsider their dependency on Google services (and there are a lot of companies that would be happy to get these customers) b) Is easy to circumvent by using Chrome for Google services and Firefox/whatever for anything else.