When I have view markup like the following, and then try to tab between the two ace:textEntry fields:
{code}
<?xml version="1.0" encoding="UTF-8"?>
<f:view xmlns="http://www.w3.org/1999/xhtml" xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html" xmlns:ace="http://www.icefaces.org/icefaces/components">
    <h:head />
    <h:body styleClass="icefaces3-portlet ltr">
        <h:form id="f1">
            <ace:textEntry id="firstName" required="true" value="#{applicantModelBean.firstName}" />
            <ace:textEntry id="lastName" required="true" value="#{applicantModelBean.lastName}" />
        </h:form>
    </h:body>
</f:view>
{code}

... then Chrome reports the following error:
Uncaught ReferenceError: setFocus is not defined ice3:1
(anonymous function) ice3:1
b.event.dispatch ice3:16
b.event.add.bE.handle.bC

Adding the icefaces-compat dependency to the project fixes the problem. I think this might reveal a JavaScript dependency of the ACE components on the Compat components?