1. A method for session-based matching of mutable browser identifiers, the method comprising: storing information in memory regarding: a plurality of mutable browser identifiers, and one or more maps, wherein each map associates an immutable browser identifier with one or more mutable browser identifiers, the immutable browser identifier unique to an associated browser; receiving information from a computing device that has used a browser to download a website, wherein the downloaded website includes a reference to a mutable browser identifier specific to the downloaded website; identifying that the referenced mutable browser identifier corresponds to one of the stored mutable browser identifiers based on a comparison of session information in the received information to session information associated with the corresponding stored mutable browser identifier; and mapping the referenced mutable browser identifier to the corresponding stored mutable browser identifier.