User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.88 Safari/537.36

Steps to reproduce:

I ran test code for testing [0].

An error occurs in this position[1].
When It is not doing anything, getCurrent() result be returned follow as:
{ colors: null, images: null, properties: null, }
(Also, I attach a picture of getCurrent() results)
Object.keys(returnedTheme).length result is "3", cannot be "0".
So It happens failure.

[0]
./mach test toolkit/components/extensions/test/browser/browser_ext_themes_dynamic_getCurrent.js

[1]
https://dxr.mozilla.org/mozilla-central/rev/1c9b97bed37830e39642bfa7e73dbc2ea860662a/toolkit/components/extensions/test/browser/browser_ext_themes_dynamic_getCurrent.js#109-110

Actual results:

The test code fails.

Expected results:

The test code should be passed.

This is a meaningless report.
I will solve this problem in another report(https://bugzilla.mozilla.org/show_bug.cgi?id=1581886).
Sorry, Can you close this report for me?

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