(New Map Viewer) Step 1 – Add WFS Service Connection

• Launch ArcGIS Online (New Map Viewer).
• Create New Map.
• Click on (+) in the top left corner.
• Select 'OGC WFS web service'.

(New Map Viewer) Step 2 - Establish Connection

• For server URL set WFS Connection/URL enter connection string for the desired WFS. For example, for the last 7 day WFS services for the continental US and Hawaii use https://firms.modaps.eosdis.nasa.gov/mapserver/wfs/USA_contiguous_and_Hawaii/<YOUR_MAP_KEY>/? where ‘YOUR_MAP_KEY’ is the unique code containing both letters and numbers
  (make sure '/?' is included at the end of your WFS URL).
• If connection was successful, there will be a list of FIRMS WFS service feature layers.
• Select the layer of interest (ex. NOAA-20 7 days fires).
• Click on 'Add to map'

(New Map Viewer) Step 3 - View FIRMS Layer

(Map Viewer Classic) Step 1 – Add WFS Service Connection

• Launch ArcGIS Online (Map Viewer Classic).
• Create New Map.
• Click on 'Add' in the top navigation bar.
• Select 'Add Layer from Web'.

(Map Viewer Classic) Step 2 - Establish Connection

• For server URL set WFS Connection/URL enter connection string for the desired WFS. For example, for the last 7 day WFS services for the continental US and Hawaii use https://firms.modaps.eosdis.nasa.gov/mapserver/wfs/USA_contiguous_and_Hawaii/<YOUR_MAP_KEY>/? where ‘YOUR_MAP_KEY’ is the unique code containing both letters and numbers
  (make sure '/?' is included at the end of your WFS URL).
• If connection was successful, there will be a list of FIRMS WFS service feature layers.
• Select the layer of interest (ex. NOAA-20 7 days fires).
• Click on 'Add to map'

(Map Viewer Classic) Step 3 - View FIRMS Layer

• In 'Content' tab, find your FIRMS layer and click on (...)
• Select 'WFS OGC Options'
• Turn on 'swap X/Y coordinates'