(In reply to Frederik Braun [:freddy] from comment #2)
There's something with comment 0, that I don't understand. First, you talk about the triggeringPrincipal required for QueryTriggeringPrincipal which in turn gives us the right contentpolicytype. However, the Bug 1319908 you mentioned which should have added the attribute set the loadingPrincipal, not the triggeringPrincipal.
I don't know enough about principals to answer this question, but I did find this changeset which landed after bug 1319908 and made
GetContentPolicyTypeForUIImageLoading use the triggering principal instead of the loading principal.
Can you expand on what exactly you see with favicon loads that do not succeed?
I don't see any errors or bad behavior. I only noticed code that doesn't do anything, and which might no longer work as intended, so I wanted to call attention to it.
I've removed the unused
mContentType fields from the native menu icon loading code in D104634; maybe there is more code that can be removed.
Maybe Gecko logging with
CSMLog:5 could give us the amount of detail we'd need (should print principals and contentpolicytypes for all outgoing requests, so it will be noisy)
I can get a log with that tomorrow, if it's interesting.