We need to set the pref devtools.application.enabled to true by default on Nightly

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&group_state=expanded&resultStatus=testfailed%2Cbusted%2Cexception&revision=17f7eac615fa61821cce3dafcbfc80110bfaa69d&selectedJob=285402444&searchStr=Linux%2C18.04%2Cx64%2Cdebug%2CMochitests%2Ctest-linux1804-64%2Fdebug-mochitest-devtools-chrome-e10s-3%2CM%28dt3%29

Failure log: https://treeherder.mozilla.org/logviewer.html#?job_id=285402444&repo=autoland

Backout link: https://hg.mozilla.org/integration/autoland/rev/3c3ef2e5eea0729acc216e5b1e2bd602e8cb015d

[task 2020-01-17T17:55:56.961Z] 17:55:56 INFO - TEST-PASS | devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js | Correct event for dom was fired -
[task 2020-01-17T17:55:56.961Z] 17:55:56 INFO - Buffered messages finished
[task 2020-01-17T17:55:56.961Z] 17:55:56 INFO - TEST-UNEXPECTED-FAIL | devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js | Tab for registered tool dom is present in first toolbox -
[task 2020-01-17T17:55:56.961Z] 17:55:56 INFO - Stack trace:
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochikit/content/browser-test.js:test_ok:1292
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js:checkRegistered:106
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js:toggleTool:83
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js:testToggleTools:52
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js:null:16
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochikit/content/browser-test.js:Tester_execTest/<:1062
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochikit/content/browser-test.js:Tester_execTest:1097
[task 2020-01-17T17:55:56.962Z] 17:55:56 INFO - chrome://mochikit/content/browser-test.js:nextTest/<:925
[task 2020-01-17T17:55:56.963Z] 17:55:56 INFO - chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:SimpleTest.waitForFocus/waitForFocusInner/focusedOrLoaded/<:808
[task 2020-01-17T17:55:56.963Z] 17:55:56 INFO - TEST-PASS | devtools/client/framework/test/browser_toolbox_options_multiple_tabs.js | Checkbox for registered tool dom is checked in first toolbox -

Please take a look over this dt3 on browser_toolbox_toolbar_reorder_by_dnd too https://tinyurl.com/sdfwmlb.

Backed out for failures on browser_toolbox_dynamic_registration.js

backout: https://hg.mozilla.org/integration/autoland/rev/cd02b96bdce57d9ae53b632ca4740c871d3ecc32

push: https://treeherder.mozilla.org/#/jobs?repo=autoland&group_state=expanded&searchStr=linux%2C18.04%2Cx64%2Casan%2Copt%2Cmochitests%2Ctest-linux1804-64-asan%2Fopt-mochitest-devtools-chrome-e10s-7%2Cm%28dt7%29&revision=f6ccc4ba38d942c3d2c4f5a7e9b08dc096714fd9&selectedJob=285837860

failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=285837860&repo=autoland&lineNumber=1761

[task 2020-01-21T21:38:07.837Z] 21:38:07 INFO - TEST-PASS | devtools/client/framework/test/browser_toolbox_dynamic_registration.js | tool-registered event handler sent tool id -
[task 2020-01-21T21:38:07.838Z] 21:38:07 INFO - TEST-PASS | devtools/client/framework/test/browser_toolbox_dynamic_registration.js | tool added to map -
[task 2020-01-21T21:38:07.839Z] 21:38:07 INFO - Buffered messages finished
[task 2020-01-21T21:38:07.840Z] 21:38:07 INFO - TEST-UNEXPECTED-FAIL | devtools/client/framework/test/browser_toolbox_dynamic_registration.js | new tool's tab exists in toolbox UI -
[task 2020-01-21T21:38:07.840Z] 21:38:07 INFO - Stack trace:
[task 2020-01-21T21:38:07.842Z] 21:38:07 INFO - chrome://mochikit/content/browser-test.js:test_ok:1292
[task 2020-01-21T21:38:07.842Z] 21:38:07 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_dynamic_registration.js:toolRegistered:37
[task 2020-01-21T21:38:07.843Z] 21:38:07 INFO - resource://devtools/shared/event-emitter.js:newListener:154
[task 2020-01-21T21:38:07.843Z] 21:38:07 INFO - resource://devtools/shared/event-emitter.js:emit:195
[task 2020-01-21T21:38:07.844Z] 21:38:07 INFO - resource://devtools/shared/event-emitter.js:emit:276
[task 2020-01-21T21:38:07.844Z] 21:38:07 INFO - resource://devtools/client/framework/devtools.js:registerTool:149
[task 2020-01-21T21:38:07.845Z] 21:38:07 INFO - chrome://mochitests/content/browser/devtools/client/framework/test/browser_toolbox_dynamic_registration.js:testRegister:20
[task 2020-01-21T21:38:07.845Z] 21:38:07 INFO - TEST-PASS | devtools/client/framework/test/browser_toolbox_dynamic_registration.js | new tool's panel exists in toolbox UI -

https://hg.mozilla.org/mozilla-central/rev/d68d052eabc5
https://hg.mozilla.org/mozilla-central/rev/5ae1f3f907cd

Should that be noted in our Nightly release notes?

Should that be noted in our Nightly release notes?

I'm pinging Harald about this

Release Note Request (optional, but appreciated)
[Why is this notable]: New manifest and service worker debugging capabilities
[Affects Firefox for Android]: No
[Suggested wording]: Service Workers and Web App Manifests are easier to inspect in DevTools' new Application panel, which also integrates into the newly landed Service Worker debugging capabilities.
[Links (documentation, blog post, etc)]: TBD

Note added to our 74 Nightly release notes, thanks.

Removing the relnote flag, this should happen in bug 1642947 when this ships to release instead.