could be my mouse but other browsers do not have this behaviour. anyway i found this Smooth Scroll extension and am gonna see if it helps.
Yes, there seems to be some issue with newer SRWare versions and Logitech mice.
With the older portable Iron 3.0.197 there was no issue, but with portable Iron 4.0.280 my mouse movement was seriously impaired-- to the point Iron was completely unuseable.
I now have both the older and newer portable SRWare versions running smoothly on my system. Can't comment on any issues with this latest beta.
Unfortunately, I'm not exactly sure what change I made to "fix" the mouse issue. Strange as I know this is gonna sound--try running Iron in Sandboxie to see if there's any change in mouse function. All I know is it worked for me.