Ubuntu :: Spinning Cursor After Firefox Loads

What I have noticed on several versions of Ubuntu, both 32 and 64 bit (including 9.10, 10.04 b2 and UNR 9.10) is that after the launch of Firefox (including the current 3.6.3 version), I continue to get a spinning cursor for more than 10 seconds after the FF window is present and ready to accept input. Sometimes I get it only when moving the cursor outside the FF window and other times it will be in the window, too. I have even noticed it persist for a short time after quitting FF. I think it's definitely related to FF because I don't see this occur unless FF is launched, not even when another browser (Chromium in this case) is launched. To add to the mystery, I see it in Ubuntu and Mint 8 xfce, but not in Ubuntu-based distros with simpler window managers like Mint 8 fluxbox or CrunchBang 9.04 (openbox). To try to get rid of this, I have tried various FF configuration speedups available from the Net - changes implemented through about:config. These do speed up FF, but they don't get rid of the spinning wheel.As far as I can tell, the spinning wheel has no impact on FF operation - it doesn't stop me from entering a url and accessing it, though perhaps it slows down implementation.