correctly load scripts in chrome & firefox #5342

Job	Run time
Test	2m 15s
Build extensions	5m 39s
ember-try (ember-lts-3.16)	1m 30s
ember-try (ember-lts-3.20)	1m 15s
ember-try (ember-lts-3.24)	1m 43s
ember-try (ember-lts-3.28)	1m 36s
ember-try (ember-release)	1m 21s
ember-try (ember-beta)	1m 22s
ember-try (ember-canary)	1m 41s
ember-try (ember-default-no-prototype-extensions)	1m 7s
Publish Firefox extension	0s
Publish GitHub release	0s
Publish bookmarklet	0s
Publish Chrome extension	0s
Publish npm package	0s
	19m 29s

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