I was pleased to discover that after a mere 9 years
Yup, 9 years, I couldn’t believe the time either, see for yourself:
What this means is that Firefox finally has a feature
that Internet Explorer has had since version 4 (1997)
(it was made a standard by W3C HTML 4.01 in December 1999)
(the repeat of the word is simply because of modern validation standards, without it the validation nutters have conniptions)
This causes the script to delay executing until the page is loaded. In some cases the script is also delayed in loading. The short answer is it will make your page seem to load faster for your visitors.
(if you removed the DEFER it would show “hello world” as expected)
I still don’t know what the status of webkit/safari/chrome is on DEFER or Opera for that matter, much more googling required.