Angular 1.6, $http.post not working in Firefox - angularjs

Question

I'm trying to make a simple Angular "$http.post" request to a basic registration REST API, but when I check the network tab (developer tools) in Firefox, the POST request is missing.
$http.post('http://example.com/api/user/userregistration', $scope.userInfo).then(function successCallback(response){
console.log(response.data.object, status);
$scope.processing = false;
$scope.processed = true;
},function errorCallback(response){
console.log(response.config, response.data);
});
I do see a HTTP OPTIONS pre-flight request with 200 OK response, but no subsequent POST request seems to work.
I also tried making a Jquery Ajax POST request to the same API but to no avail.
The same Angular code works perfectly fine in Chrome & Safari (OSX Sierra).
I have attached the screenshot of the OPTIONS request which is returning 200 OK but the subsequent POST request is missing (no errors in console)
Please help troubleshoot the above and suggest if I'm missing something obvious.

Answer 1

Ok found the problem and solved it.
The problem:
The Firefox browser installed in my OSX machine was not showing any error, hence I was unable to troubleshoot.
Checked the same POST request from a Firefox in Windows machine, fortunately saw an error saying:
Cross-origin request blocked. (Reason: invalid token "multipart/form-data" in CORS header "Access-Control-Allow-Headers")
The above error means Firefox does not treat "multipart/form-data" as a valid entry in "Access-Control-Allow-Headers" HTTP response header. (However, Chrome & Safari seem cool about it!)
The Solution:
Removed "multipart/form-data" from the "Access-Control-Allow-Headers" HTTP response header and Voila it worked in Firefox as well!