Firefox no longer remembers order of windows!

I wrote:

> Another change is that on restart it displays windows in the same order as
> previously, so I no longer have to waste time re-ordering windows after
> restarting firefox, and I don't need "xprop -set WM_NAME" to help me find
> what I want after the windows come up wrongly ordered.

I've just checked this and it is no longer true! My windows were restored
in a random order. Very annoying. I wonder if I have done something
different.

Aaron