Backendless and Firebase, both being mobile backend as a service (MBaaS) platforms, present different capabilities for mobile app creation.
Here is a list of the Backendless features which either are not supported by Firebase or just exceed it in usability.

GET https://api.backendless.com/<appid>/<REST API key>/data/Movie?props=Sum(totalBoxOffice)
The output is an object with the sum property:
[
   {
       "sum": 14507795640,
       "___class": "Movie"
   }
]
Backendless also supports results grouping for a column. This column can either be found in the original or linked table. For example, the following query will display the sum of all orders, grouped by country:
GET https://api.backendless.com/<app id>/<REST API key>/data/Orders?props=Sum(orderAmount)&groupBy=relatedCountry.countryName
The output for this request is a collection of objects, any of which contains the total amount of orders for a particular country:
[
 {
   "sum": 1324231,
   "countryName": "Italy",
   "___class": "Orders"
 },
 {
   "sum": 5675675,
   "countryName": "France",
   "___class": "Orders"
 },
 {
   "sum": 2342234,
   "countryName": "Ireland",
   "___class": "Orders"
 }
]
You can also add a filter to the grouped objects using the having condition. The following query will return only groups of countries with the total amount of orders > 10000. The output for this request is a collection of objects, any of which contains the total amount of orders for a particular country:
GET https://api.backendless.com/<app id>/<REST API key>/data/Orders?props=Sum(orderAmount)&groupBy=relatedCountry.countryName&having=Sum(orderAmount)>10000
It is worthwhile to point out the following: