The list box is not letting us set a width. By “list box” I mean the box that pops up with the auto complete results. Checking in firefox it looks like the width is set in the “style” attribute rather than through the class?
By default size of list reflect the size of related combobox input ( because it reflects changes of different element it can’t be set from css )
If necessary you can switch it to auto size behavior by adding next line
combo.autoOptionSize=true;
Any other behavior can be achieved only be code modification.