What many of these tests have in common is that they involve updated extension schemas.
I suspect that the schema updated are not correctly processed because part of the schemas / registrations are stored in StartupCache.
In bug 1783828, I have shown that the consequence of this is that any change to an extension API schema is going to result in a test failure, and that the failure may disappear once the conditioned profile has been updated in 1~2 days. E.g. because of:
This is a condprof test-only issue. In Firefox, the StartupCache is wiped whenever a new version is released. That logic is triggered from https://searchfox.org/mozilla-central/rev/c0bed29d643393af6ebe77aa31455f283f169202/toolkit/xre/nsAppRunner.cpp#5178-5181, e.g. wiped when the app version info in the profile directory's
compatibility.ini does not match the application version. The caller of this is ultimately
XRE_main, which is called by Firefox on desktop and Android, but not by xpcshell (
To test whether the startupcache may be affecting test results, run the condprof tests with
MOZ_PURGE_CACHES=1 environment variable to forcibly clear the caches.