I do not think it is possible yet, but there is a workround you could use:

See /questions/951419 where kbrosnan suggests

There are no direct way to set a home page. That being said there is a way to get the same effect.

   Make sure that the page is in your history
   Tap in the address bar
   Search for the history item
   Long press on the history item
   Select "Add to home screen"
   Use this bookmark shortcut to launch Firefox.

hello, create a bookmark for google.com on the homescreen of your device.