dbFront supports HTML formatted fields but it has no direct support for RTF fields.
One work-around is to convert the field type to VarBinary or Blob. dbFront treats VarBinary or Blob fields as attachments and allows users to download the contents for viewing. When combined with an RTF viewer browser extension, this allows users to view the RTF contents directly in their browser.
NOTE: Please vote on this Feature Request if you want dbFront to include an integrated RTF viewer.