It's a "Mork" file and I can't make any sense of crazyman's documentation, such as it is. I asked on IRC #mozilla, and all I got was some random guy writing a term paper on the computer industry who wanted to interview me about the "good old days."
(Just grepping it for URLs isn't enough, because I also want the date associated with loading them, and the stuff in that file appears to be in hash order or something. There seems to be a maze of half a dozen overlapping numerical namespaces, all alike.)
Update: I've got something that almost works now, but it's really slow: mork.pl.