I had experienced this today and looked into it a little when I found this bug report already here. Disabling all plugins and extensions, this behavior still happens, and I have seen it on every Karmic machine I have tried. To me, it seems to be an issue with startup notification, as eventually the mouse cursor does return to normal (there is a timeout for startup notification) but clearly this is only happening with firefox. I also understand the sentiment of the first reporter who found it annoying.
I had experienced this today and looked into it a little when I found this bug report already here. Disabling all plugins and extensions, this behavior still happens, and I have seen it on every Karmic machine I have tried. To me, it seems to be an issue with startup notification, as eventually the mouse cursor does return to normal (there is a timeout for startup notification) but clearly this is only happening with firefox. I also understand the sentiment of the first reporter who found it annoying.