Several Firefox 16 users have confirmed a situation in Firefox 16.0.1 that was not present in 15.
When an "input" and "select" element appear together on the same page as a "setTimeout", scrolling the window hangs at the "select" when using the scrollbar slider, but not when clicking the arrows or scrollbar background. A lean test case is provided here (source in top pane, execution in bottom pane:
Moving and separating the "input" from the "select" can relieve the problem in some scenarios, mostly, I think, when the two are in separate forms or are in separate block containers, but I didn't investigate deeply.
Not looking for a solution, just reporting.
I realize that this should be reported to the bug site, but I don't have a throw-away email. If someone else could report, that would be great.
It appears that the interval length is relevant. Using a longer interval such as 500 milliseconds, you can move the scroll thumb briefly before it freezes again. It's difficult to imagine what computation is being affected by this precise combination of fields.
I had also played with the interval and noticed that difference. I find the connection between the two bizarre. Could the browser be attempting to set focus?
In researching, I also found an earlier report on Mozilla (sorry, don't recall where) in which the "select" or "multi-select" wasn't scrolling entirely, and I suppose a fix to that issue might have had consequences in this new scenario. Or perhaps this is part of that issue in some way.
Anyway, I'm not a Firefox geek and I don't have enough system resources to play with versions, so my best effort was to attempt to bring the problem to Mozilla. If someone here can manage the bug reporting, that would be great. :-)