User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:73.0) Gecko/20100101 Firefox/73.0

Steps to reproduce:

I attempted to make an XMLHttpRequest to one of our APIs from a persistent background script in our Firefox Addon and I unexpectedly got an error because of a "null" Origin. I'm also able to reproduce this with the fetch() API.

Minimal test case attached.

Actual results:

"Origin: null" was sent in the header.

The following error occurred:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://events-api.mix.com/v1/t. (Reason: CORS header ‘Access-Control-Allow-Origin’ does not match ‘null’).

Expected results:

"Origin: moz-extension://HASH" should have been sent in the header

No error should have occurred

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Reproduced the issue on latest Firefox Nightly 74.0a1 (2020-01-09) (64-bit) and Beta 73.0b2 (64-bit) on Windows 10 x64.
This seems like a recent regression, it works well on the latest Release 72.0.1 (64-bit).
Attached screenshots for reference.

Thanks for the report anoakie!

Ah, this seems like a Duplicate of Bug 1607154.
Regression range found using this testcase: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=0f6958f498427fad830cdf94e279d8acd16402c9&tochange=f09f24f2b545919ab0db4bd352c276779c58bcc6

Regression range contains Bug 1405971 which causes this issue.
Closing it as duplicate.

Sorry for the spam, forgot to correct component.