document.designMode is a cool feature.

Perhaps not a very well known feature, hence this heads-up ;)

By enabling it in console ( document.designMode = 'on' ), you can edit and experiment with a page content right from the browser.

No need to change code on IDE. No refresh. Just live, fresh mangling. yay!

Check it out:

document.designMode in action on

Read more on Mozilla docs.

This post is also available on DEV.