Last week we turned on tests for Apple Silicon (OSX 11.2.3 on new Apple based hardware). We are using the simplified new test config process:
https://firefox-source-docs.mozilla.org/testing/ci-configs/index.html

As the tests are live, we are now filing bugs to help close the loop and hope to fix any issues over the next 7 weeks. As the process outlines, there are tier-3 jobs running on m-c which run these skipped tests and will expect a failure/timeout/crash- if it doesn't fail, then the job will turn orange.

here is the failing test:
security/sandbox/test/browser_content_sandbox_fs.js

:gcp, I wanted to make you aware of a test that is skipped on the new apple silicon platform- please triage this as you see fit.

(In reply to Joel Maher ( :jmaher ) (UTC -0800) from comment #1)

:gcp, I wanted to make you aware of a test that is skipped on the new apple silicon platform- please triage this as you see fit.

Thanks. I'll take this.

as an update, we disabled the tests yesterday to update the OS and ensure we are running everything in the right arch (x86_64 vs arm64). we will update the bug when things are coming back online.

New log for this available on https://treeherder.mozilla.org/jobs?repo=mozilla-central&tier=1%2C2%2C3&searchStr=macosx1100&revision=eac40293649628d32911c909219d514bebb8ce63&test_paths=security%2Fsandbox%2Ftest&selectedTaskRun=R4y3QBtnRay_cAxo-rZATg.0

INFO - TEST-UNEXPECTED-FAIL | security/sandbox/test/browser_content_sandbox_fs.js |
/private/var/folders/xh/5_nnbb2s7y9c1sv4zwl_ckk0000014/C/com.apple.FontRegistry/font exists - false == true -
JS frame :: chrome://mochitests/content/browser/security/sandbox/test/browser_content_sandbox_fs_tests.js :: 
testFileAccessMacOnly :: line 283

I don't know when, but at some point the /private/var/folders/.../C/com.apple.FontRegistry/font file became no longer present on our 10.15 test installations and the test optimistically assumes it is present. The test was added with the fix for bug 1692220 and its purpose is to ensure the sandbox allows read access to the font file. If the file is not present, that particular test should be skipped. Files in the cache dir are not guaranteed to be present.

Change browser_content_sandbox_fs.js to not assume the font registry directory or the 'font' file have been created by the system. If the directory and or file are not present, skip the readability test instead of failing.

https://hg.mozilla.org/mozilla-central/rev/39d0b269e248