1. One or more non-transitory computer-readable storage mediums storing one or more sequences of instructions for transferring a file using a virtualized application, which when executed by one or more processors, cause: executing the virtualized application within a first isolated environment executing on a physical machine; upon the virtualized application receiving an instruction to download one or more files stored external to the physical machine, the virtualized application requesting, from a second isolated environment, information identifying at least a portion of a file system, maintained by said second isolated environment, which is visible to said first isolated environment; after said first isolated environment receiving said information from said second isolated environment, said first isolated environment generating an appearance of an interface that enables said at least portion of the file system, maintained by said second isolated environment, to be browsed while preventing files stored within the first isolated environment to be browsed; upon the second isolated environment receiving display data from the first isolated environment, the second isolated environment displaying the interface rendered by the first isolated environment, wherein said display data describes said appearance of said interface; and upon the virtualized application receiving input, from said interface, identifying a target location within said file system, the virtualized application storing said one or more files at said target location.