I'm getting this same problem while trying to set my profile at the welcome screen (or by going to settings). This is on Firefox Developer Edition.
I then manually disabled CORS (I overrode it with an extension), and noticed it was failing again, but this time with an HTTP 413 to the API endpoint. I changed my image to something smaller (it was 3 MB), and it worked.
I then manually disabled CORS (I overrode it with an extension), and noticed it was failing again, but this time with an HTTP 413 to the API endpoint. I changed my image to something smaller (it was 3 MB), and it worked.