that is why i need to re-inject code into the DOM of the page from my popup.html . Is every finite group the outer automorphism group of a finite group? function x(){/*whatever you want to run here*/} Transfer control from popup to content script - Google Chrome Extension, Disabling Chrome cache for website development, Getting Chrome to accept self-signed localhost certificate. . But nevertheless this is a workaround and I am really interested in which browser has a bug here. https://bugs.chromium.org/p/chromium/issues/detail?id=792420. var filter = {}; In Chrome the CSS could not be parsed on execution time and I see "Times New Roman" see Chrome If you check the developer tools, DOMContentLoaded has been fired differently in Chrome and Firefox. External style sheets don’t affect DOM, and so DOMContentLoaded does not wait for them. Why is Olympus Mons the largest volcano in the whole solar system? How should I tell manager? For full details on this event please see the page on the Document: DOMContentLoaded event. The DOMContentLoaded event is also blocked on the DOM parser. If you need to run something encapsulated inside the defer (pseudo code): . But nevertheless this is a workaround and I am really interested in which browser has a bug here. https://bugs.chromium.org/p/chromium/issues/detail?id=792420. var filter = {}; In Chrome the CSS could not be parsed on execution time and I see "Times New Roman" see Chrome If you check the developer tools, DOMContentLoaded has been fired differently in Chrome and Firefox. External style sheets don’t affect DOM, and so DOMContentLoaded does not wait for them. Why is Olympus Mons the largest volcano in the whole solar system? How should I tell manager? For full details on this event please see the page on the Document: DOMContentLoaded event. The DOMContentLoaded event is also blocked on the DOM parser. If you need to run something encapsulated inside the defer (pseudo code):