I bet this is a common question among ADF developers who wish to have their own favicon for their page

Please follow the steps to achieve the same

add the following facet to the af:document tag of your adf page

<af:document id="d1">
..
..
..
<f:facet name="metaContainer">
 outputText escape="false"
 value='png" href="#{facesContext.externalContext.requestContextPath}/favicon.ico">' id="o1"/>
 </f:facet>
</af:document>

please note that the favicon specified in the value attribute in the outputext should be in the root-level of your web application