Changed to use strict equality and inequality and single quotes for strings

I ran into an error before which I can't remember now what it was exactly, but what I did to fix it was use `===` and `!==` instead of `==` and `!=` which as a rule is a best practice in general. 

I think the error had to do with passing an object vs an array, eg:

`angularFire(usersurl, $scope, 'users', {});`
vs
`angularFire(usersurl, $scope, 'users', []);`

But, I may be remembering the wrong thing. Either way, I've used the strict equality now for a while without any problems.