I think we should use a pref in docshell to fail loadURI loads when a triggeringPrincipal is implied. Example code change: https://hg.mozilla.org/try/rev/a4d04fffb025b25e1e74e6c182cbdcc353d519be The idea is to rollout the pref only to beta and nightly opt builds and wait a release cycle before removing the implied triggering principal code from DocShell: https://searchfox.org/mozilla-central/rev/1ce4e8a5601da8e744ca6eda69e782318afab54d/docshell/base/nsDocShell.cpp#942-951 This allows us to verify with a wider audience before removing the implied triggeringPrincipal code for an opt build.

:bz / :bholley do you have any views on doing this?

Seems reasonable to add a pref and try it on nightly, for sure.

I'm not in the loop on the particular code change, but the strategy in general sounds sensible.

Pushed by jkingston@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/c5cf88fb02d1 add in user pref to prevent loading implied triggeringPrincipal loads for dev and nightly builds. r=ckerschb

Backout by ebalazs@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/2f86f12badc1 Backed out changeset c5cf88fb02d1 for causing multiple failures e.g. browser/extensions/formautofill/test/mochitest/test_address_level_1_submission.html CLOSED TREE

Backed out changeset c5cf88fb02d1 (Bug 1498526) for causing multiple failures e.g. browser/extensions/formautofill/test/mochitest/test_address_level_1_submission.html CLOSED TREE Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Crunnable&revision=c5cf88fb02d1a5b8c17bc415058b09a7e308a582&selectedJob=210051089 Failure log examples: https://treeherder.mozilla.org/logviewer.html#?job_id=210051089&repo=autoland&lineNumber=3714 https://treeherder.mozilla.org/logviewer.html#?job_id=210045955&repo=autoland&lineNumber=1732 https://treeherder.mozilla.org/logviewer.html#?job_id=210044781&repo=autoland&lineNumber=2435 https://treeherder.mozilla.org/logviewer.html#?job_id=210045521&repo=autoland&lineNumber=8515 https://treeherder.mozilla.org/logviewer.html#?job_id=210045766&repo=autoland&lineNumber=20643 Backout push: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Crunnable&classifiedState=unclassified&revision=2f86f12badc1e86b772e8dd95b4f6ff7e60b2d6e

Fixed, I was being overzealous with adding the failures in. Try push of the update here: https://treeherder.mozilla.org/#/jobs?repo=try&revision=42887c4f8048f51678cb67d06385bc27bd0deeba

Pushed by jkingston@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/34938b2824ca add in user pref to prevent loading implied triggeringPrincipal loads for dev and nightly builds. r=ckerschb