In web-platform-tests, there are 9 of 12 tests which are expected TIMEOUT or fail. Most of these are found with origin in the filename.

https://searchfox.org/mozilla-central/source/testing/web-platform/meta/html/user-activation

locally on windows10, I verified a failure running:
./mach wpt testing/web-platform/tests//html/user-activation/consumption-sameorigin.tentative.html

and saw this in the ./mach console:
0:55.97 TEST_START: /html/user-activation/consumption-sameorigin.tentative.html
0:56.58 pid:24176 JavaScript error: http://web-platform.test:8000/html/user-activation/resources/child-one.html, line 6: TypeError: can't access property "isActive", navigator.userActivation is undefined
0:56.59 pid:24176 JavaScript error: http://web-platform.test:8000/html/user-activation/resources/consumption-sameorigin-child.html, line 7: TypeError: can't access property "isActive", navigator.userActivation is undefined
0:56.67 pid:24176 JavaScript error: http://web-platform.test:8000/html/user-activation/resources/child-two.html, line 6: TypeError: can't access property "isActive", navigator.userActivation is undefined
1:06.55 TEST_END: Test TIMEOUT. Subtests passed 0/8. Unexpected 0

I am thinking we don't support userActivation?

:hsinyi, can you find someone to look at these tests and determine if there is anything we can do to get them passing or indicate if this is not supported?

Edgar can help answer the question and suggest the next step. :)

We don't support navigator.userActivation, the API is not defined in spec yet, see bug 1591902 and https://github.com/whatwg/html/pull/4009.

Sounds like this should be implementation-status: backlog unless we have a standards-position that the proposal is harmful.

As Edgar mentioned, the API isn't even in the spec and the tests are tentative.

run html/user-activation/ tests as backlog (tier-2)

https://hg.mozilla.org/mozilla-central/rev/4ce2f172f0d2