Steps to Reproduce

run the attached example add-multiple.zul
click the 4 buttons and profile/compare the render timings

Current Result

the first 2 buttons take ~1.3 seconds to render/resize
the "workaround" buttons only take ~40ms

Expected Result

equal/equivalent render times, if possible

Debug Info

Currently only happens on chrome.

The listbox with many rows/columns is only added to highlight the performance drain, which gets worse in more complex UIs.

Root Cause

the components are added one by one, calling firesized after each component, leading to "Forced reflows"

Workaround

Appending the components into an initially invisible component or as a batch with a common parent avoids the loop of "Forced reflows"