I actually was looking for information on how to enable this feature as I had thought it had become disabled with the newer Firefox releases. For those who are not familiar with autoscrolling, it allows you to quickly scroll through a page by clicking the mouse scroll wheel and then moving the mouse up or down. When autoscroll is activated, the mouse cursor changes to this:
For those who use their middle button for other uses and can not control the behavior via their mouse software (more on this shortly), the autoscrolling can be disabled in most all versions of Firefox via:
- Windows: Tools >> Options… >> Advanced >> in the Browsing section, un-check Use autoscrolling
- Linux: Edit >> Preferences >> Advanced >> in the Browsing section, un-check Use autoscrolling
- Mac: Firefox >> Preferences… >> Advanced >> in the Browsing section, un-check Use autoscrolling
After some more searching (which lead to me finding some for mouse-wheel related tweaks), I found that my mouse software had the mouse-wheel click set for zoom.
The Firefox Extension Guru's Blog 
[…] El Guru @ 4:13 AM I came across these tweaks while searching for a solution on how to fix my issue with autoscrolling (which turned out to be a software issue, not Firefox). I’ll admit that I never really use […]