Starting with version 9.0.1 of IBM Notes / Domino,a new managed bean called the deviceBean is  introduced within the XPages run-time to provide an easy to use and easy to program way of identifying a popular range of mobile and tablet devices directly within ServerSide JavaScript or Expression Language (EL) computed expressions.

So, instead of using

<xp:text escape="true" id="computedField2"
value="#{javascript:context.getUserAgent().isFirefox()}"/>

you can use EL in your XPage

<xp:text escape="true" id="computedField1"
value="#{deviceBean.firefox}"/>

Read all about this new bean in the “What’s new in IBM Domino Designer 9.0.1 Social Edition?” section of the IBM Notes Designer Help