1. A computer-implemented method comprising: as implemented by one or more computing devices configured to execute specific instructions, allocating different respective portions of a volatile memory to different respective tabs of a browser application, wherein each tab displays a different content item loaded by the browser application, and wherein the browser application has a user interface that enables a user to select a content item to view by selecting the tab in which the content item is loaded; determining that a memory state of a first content item loaded in a first tab of the browser application has changed, said memory state corresponding to a volatile memory portion allocated to the first tab; serializing, by the browser application, the memory state of the first content item based at least partly on the determination that the memory state of a first content item has changed, wherein serializing the memory state comprises translating object state data stored in the volatile memory portion into a format for storage in non-volatile storage, and storing the translated object state data in non-volatile storage, wherein serializing the memory state of the first content item comprises storing data regarding a memory state of one or more portions of the first content item, and wherein one or more additional portions of the content item are excluded from the serialization in response to determining that a memory state of the one or more additional portions has not changed; after serializing the memory state, releasing the allocation of the volatile memory portion to the first tab, such that at least a portion of the volatile memory portion is made available for use other than to store data corresponding to the first tab; after releasing the allocation, continuing to display a representation of the first tab in the user interface of the browser application; and responsive to user selection of the representation of the first tab, restoring a state of the first tab, said restoring comprising de-serializing the memory state to a portion of the volatile memory corresponding to the first tab.