Comment 3 for bug 566412

I get the exact same behaviour described in this bug report. I thought I'd just give some additional information here.

The interesting thing is that it literally locks the whole system up. You'd think I could do something particularly since the mouse seems responsive and all commands made to either the keyboard or the mouse appear to queue behind the completion of the autoscroll operation. So for instance if I CTRL-Q Firefox or select any app with my mouse it will perform all of those operations as soon as the autoscoll cursor has reached the bottom of the page I started scrolling.

I can reproduce this consistently on pages with many images and seemingly at least one flash video using both 10.0.45 and 10.1 flash versions. I am running the latest updates on 10.04 upgraded from 9.10 (as opposed to clean install). Firefox is version 3.6.3. I can provide other information if desired.

Here are a few example pages that consistently produces this result given these operations listed below
http://www.sc2blog.com/2010/04/
http://abduzeedo.com/daily-inspiration-521

* enable autoscroll in Firefox if not already enabled (Edit->Preferences->Advanced->check use autoscrolling)
* go to the top of one of the example pages middle-click to enable autoscroll, move mouse down just slightly to start scrolling (I find faster scrolling speeds do not reproduce the problem)
* wait, noticing that no operation with a keyboard or mouse can stop the scrolling (be prepared to wait a while)

I find that you can start at say the first flash video and start scrolling up so that you don't have to wait as long for it to finish scrolling.

This page is an interesting counter example where there do tend to be flash videos over blog like content but I can not reproduce this problem with autoscroll: http://lifehacker.com/