Steps to Reproduce

1. run the attached zul with IE11

Current Result

when loading the page, IE11 gets stuck for a long time (over 10s) and show "~ is not responding due to long running script" warning

Expected Result

no such warning

Debug Info

1. every addChd() triggers zUtl.fireSized(child) and access offsetWidth too many time. So IE11 has to reflow and get stuck.
2. chrome also get stuck for a while when loading the page

Workaround

apply attached js