Problem <del>mostly, but not entirely,</del> solved. For <del>Arimo</del> whatever font you want to install, you need to insert this text between the &lt;familyset&gt; tags in the file /system/etc/system_fonts.xml:

    <family>
      <nameset>
        <name>the name of your font</name>
        <name>arial</name>
        <name>helvetica</name>
      </nameset>
      <fileset>
        <file>Arimo-Regular.ttf</file>
        <file>Arimo-Bold.ttf</file>
        <file>Arimo-Italic.ttf</file>
        <file>Arimo-BoldItalic.ttf</file>
      </fileset>
    </family>

And remove the designations of "arial" and "helvetica" from the Roboto entry. <del>The reason this is not entirely solved is it works only in the browser and not the HTML viewer.</del>