As an exercise in file format juggling, I made this example using the UTM grid installed with ArcGIS (a shapefile).
Convert Shapefile to JSON
This is fairly simple at ArcGIS 10.2 (new at 10.2), using the Features to JSON tool. Output is .json file.
Load JSON into Firebase
Plot Firebase data in Google Maps
Get the JSON response from Firebase using a URL like: Firebase Location + ‘.json?callback=’ + Some Function. This requests JSON from Firebase, then triggers Some Function. Inside my function, I parse the JSON into polygons, add to the map, set up infoWindows, etc.
At its worst, this is a UTM zone map. At its best, this is a way to get complex(ish) spatial data into Firebase to take advantage of the live data side of things. Have fun.