I like the comparison! Yeah, I'm not sure why it's called a leak, other than for the fact that slowly you lose available memory. Each time you opened a new tab it would require a little bit more memory. When you shut down that tab, you SHOULD get that memory freed up. But instead it wasn't, FF2 retained control of it somehow-it still had pointers to those memory segments.

So if you ran FF2 for a period of time, opening and closing tabs, eventually your machine would slow down and you would have to re-start FF2. I have had two tabs running in the past, without sound or graphics, that was taking a quarter of a gig of memory.