I have tried every upgrade since 2.21.940 and none of them work very well or don't work at all well. The latest version never erases old prefetch files, tries to erase WMIT files, 16,338MB every single time. You also still do not get a real breakdown of what the eraser is trying to do even if you click on the icon. Love 2.21.940 ...it always works well and I always know what it is doing. Sorry if that sounds like a downer but it is a fact.
Vista 32 sp2 Firefox 3.5.2
Vista 64 Ultra Firefox 3.5.2