correctly load scripts in chrome & firefox #5341

Job	Run time
Build extensions	5m 54s
Test	2m 55s
ember-try (ember-lts-3.16)	1m 13s
ember-try (ember-lts-3.20)	1m 43s
ember-try (ember-lts-3.24)	1m 14s
ember-try (ember-lts-3.28)	1m 40s
ember-try (ember-release)	1m 28s
ember-try (ember-beta)	2m 4s
ember-try (ember-canary)	1m 41s
ember-try (ember-default-no-prototype-extensions)	1m 6s
Publish Firefox extension	0s
Publish bookmarklet	0s
Publish Chrome extension	0s
Publish GitHub release	0s
Publish npm package	0s
	20m 58s

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