For the unaware, rsync is one (of many) examples of software that can compare an arbitrary directory of files of any type, and only transmit/receive the differences in the files. Doesn't matter the file type, at all.
I joked that rsync was open-source, but I have no idea if it's been ported to iOS nor how FF actually handles their file xfers. If they're just calling Apple's file transfer libraries, or Apple only allows certain ways for files to be downloaded to the devices, they may have their hands tied.
Apple is supposedly adding "delta" style App updates to iOS 5 shortly, where changes to Apps will only be the changed bits, to save on bandwidth to and from the iCloud servers, but I don't develop for iOS, so I haven't looked to see if those can be used for App data also. I doubt it, since Apple doesn't host the App data.
It was half-joking, half-serious that an implementation *might* be able to be done that would only transfer the deltas in Ye Olde Bits of the files.
The draw for FF would be a significant reduction in bandwidth utilization at their download farm, at each chart release.
But server bandwidth is so darn cheap, it's probably not enough monetary incentive to put that one very high on the priorities list. It'd make 3G only updaters very happy, though. The bottleneck (and higher price) is always at the mobile device end for bandwidth.
