Your sequence is growing, albeit at a decreasing rate, so I'm not sure it's a good fit for memory usage. Unless you meant to say the rate at which Firefox is bloating is slowing. I could believe that. But Firefox is claiming memory usage is following a sequence more like 1/2, 1/3, 1/4, ... Which should approach zero.
If you meant your sequence to represent performance, maybe that's what's happening, but then I think they should stop saying "now 1/1024 faster than before" as if it's a reason to upgrade.
That sequence was merely an example of something that is monotonic and bounded, it wasn't chosen to be a model for memory usage or performance or anything like that.
Also, I don't see Mozilla claiming memory usage follows a curve like 1/x. In fact, I don't seem them claiming anything about long term memory usage other than "it's decreasing", which is true, and can be true without implying that the memory usage will eventually be 0.
(Btw, I don't think Mozilla have ever said something as frivolous as "1/1024 faster".)
If you meant your sequence to represent performance, maybe that's what's happening, but then I think they should stop saying "now 1/1024 faster than before" as if it's a reason to upgrade.