Edit the configuration.xml file as below:

<configuration xmlns="http://www.exoplatform.org/xml/ns/kernel_1_2.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.exoplatform.org/xml/ns/kernel_1_2.xsd http://www.exoplatform.org/xml/ns/kernel_1_2.xsd">

    <external-component-plugins>

    <target-component>org.exoplatform.webui.ext.UIExtensionManager</target-component>

    <component-plugin>

        <name>add.action</name>

        <set-method>registerUIExtensionPlugin</set-method>

        <type>org.exoplatform.webui.ext.UIExtensionPlugin</type>

        <init-params>

            <object-param>

                <name>ViewSource</name>

                <object type="org.exoplatform.webui.ext.UIExtension">

                    <field name="type"><string>org.exoplatform.wiki.webui.control.MoreExtensionContainer</string></field>

                    <field name="rank"><int>1000</int></field>

                    <field name="name"><string>ViewSource</string></field>

                    <field name="component"><string>com.acme.ViewSourceActionComponent</string></field>

                </object>

            </object-param>

        </init-params>

    </component-plugin>

    </external-component-plugins>

</configuration>

Pay attention to the action name (ViewSource) and the component name (com.acme.ViewSourceActionComponent).

The configuration for UIExtension is explained here.

As noticed before, your action listener extends the MoreExtensionContainer class. Here you see it is passed to the type field. You can decide which menu your action is plugged in, by choosing one of types below: