The larger gull species are brownish when young. Yours is not all that brown, I'd guess it's a second-year gull of a species that takes four years to develop. Its legs seem pinkish (compare to yellower legs of nearby birds) which only helps a little, but if I had to guess I'd go with Herring Gull, which is very common.
Telling a young Herring from a young Glaucous, for example, is above my pay grade, but there are some experts here who may come along shortly.